diff --git a/conference.example.toml b/conference.example.toml
index 6d563ca..72f9cd0 100644
--- a/conference.example.toml
+++ b/conference.example.toml
@@ -6,6 +6,7 @@ timezone = "America/New_York"
 venue = "David L. Lawrence Convention Center, Pittsburgh PA"
 pretalx_event_slug = "pycon-us-2027"
 website_url = "https://us.pycon.org/2027/"
+total_capacity = 2500
 
 [[conference.sections]]
 name = "Tutorials"
diff --git a/src/django_program/conference/admin.py b/src/django_program/conference/admin.py
index 1d1d403..7afec2f 100644
--- a/src/django_program/conference/admin.py
+++ b/src/django_program/conference/admin.py
@@ -106,7 +106,7 @@ class ConferenceAdmin(admin.ModelAdmin):
         (
             None,
             {
-                "fields": ("name", "slug", "venue", "address", "website_url"),
+                "fields": ("name", "slug", "venue", "address", "website_url", "total_capacity"),
             },
         ),
         (
diff --git a/src/django_program/conference/management/commands/bootstrap_conference.py b/src/django_program/conference/management/commands/bootstrap_conference.py
index 793a2cc..d168000 100644
--- a/src/django_program/conference/management/commands/bootstrap_conference.py
+++ b/src/django_program/conference/management/commands/bootstrap_conference.py
@@ -41,6 +41,7 @@
     "venue": "venue",
     "website_url": "website_url",
     "pretalx_event_slug": "pretalx_event_slug",
+    "total_capacity": "total_capacity",
 }
 
 _SECTION_FIELD_MAP: dict[str, str] = {
diff --git a/src/django_program/conference/migrations/0004_add_total_capacity.py b/src/django_program/conference/migrations/0004_add_total_capacity.py
new file mode 100644
index 0000000..6d5be36
--- /dev/null
+++ b/src/django_program/conference/migrations/0004_add_total_capacity.py
@@ -0,0 +1,19 @@
+# Generated by Django 5.2.11 on 2026-02-14 03:10
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("program_conference", "0003_conference_address"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="conference",
+            name="total_capacity",
+            field=models.PositiveIntegerField(
+                default=0, help_text="Maximum total tickets across all types. 0 means unlimited."
+            ),
+        ),
+    ]
diff --git a/src/django_program/conference/models.py b/src/django_program/conference/models.py
index c37dbe8..a0b60f3 100644
--- a/src/django_program/conference/models.py
+++ b/src/django_program/conference/models.py
@@ -26,6 +26,11 @@ class Conference(models.Model):
     stripe_publishable_key = EncryptedCharField(max_length=200, blank=True, null=True, default=None)
     stripe_webhook_secret = EncryptedCharField(max_length=200, blank=True, null=True, default=None)
 
+    total_capacity = models.PositiveIntegerField(
+        default=0,
+        help_text="Maximum total tickets across all types. 0 means unlimited.",
+    )
+
     is_active = models.BooleanField(default=True)
 
     created_at = models.DateTimeField(auto_now_add=True)
diff --git a/src/django_program/manage/forms.py b/src/django_program/manage/forms.py
index 686ea76..03e601d 100644
--- a/src/django_program/manage/forms.py
+++ b/src/django_program/manage/forms.py
@@ -80,6 +80,7 @@ class Meta:
             "address",
             "website_url",
             "pretalx_event_slug",
+            "total_capacity",
             "is_active",
         ]
         widgets = {
diff --git a/src/django_program/manage/templates/django_program/manage/conference_edit.html b/src/django_program/manage/templates/django_program/manage/conference_edit.html
index ab7b5ec..63ff1ac 100644
--- a/src/django_program/manage/templates/django_program/manage/conference_edit.html
+++ b/src/django_program/manage/templates/django_program/manage/conference_edit.html
@@ -136,6 +136,18 @@ <h1>Conference Settings</h1>
       </div>
     </div>
 
+    <div class="fieldset">
+      <div class="fieldset-legend">Capacity</div>
+      <div class="form-row">
+        <div class="form-group">
+          <label for="{{ form.total_capacity.id_for_label }}">{{ form.total_capacity.label }}</label>
+          {{ form.total_capacity }}
+          {% if form.total_capacity.help_text %}<span class="helptext">{{ form.total_capacity.help_text }}</span>{% endif %}
+          {% for error in form.total_capacity.errors %}<ul class="errorlist"><li>{{ error }}</li></ul>{% endfor %}
+        </div>
+      </div>
+    </div>
+
     <div class="fieldset">
       <div class="fieldset-legend">Integrations &amp; Status</div>
       <div class="form-row--tail">
diff --git a/src/django_program/manage/templates/django_program/manage/ticket_type_list.html b/src/django_program/manage/templates/django_program/manage/ticket_type_list.html
index 0926523..974a7ae 100644
--- a/src/django_program/manage/templates/django_program/manage/ticket_type_list.html
+++ b/src/django_program/manage/templates/django_program/manage/ticket_type_list.html
@@ -12,6 +12,11 @@ <h1>Ticket Types</h1>
 {% endblock %}
 
 {% block content %}
+{% if global_capacity %}
+<div class="capacity-banner" style="padding:0.75rem 1rem;margin-bottom:1rem;border-radius:var(--radius-sm);background:var(--color-bg-alt);border:1px solid var(--color-border-light);">
+  <strong>{{ global_sold }} / {{ global_capacity }}</strong> tickets sold (venue capacity)
+</div>
+{% endif %}
 {% if ticket_types %}
 <table class="data-table">
   <thead>
diff --git a/src/django_program/manage/views.py b/src/django_program/manage/views.py
index 47746e4..a976cad 100644
--- a/src/django_program/manage/views.py
+++ b/src/django_program/manage/views.py
@@ -54,6 +54,7 @@
 from django_program.pretalx.sync import PretalxSyncService
 from django_program.programs.models import Activity, ActivitySignup, Receipt, TravelGrant, TravelGrantMessage
 from django_program.registration.models import AddOn, Order, Payment, TicketType, Voucher
+from django_program.registration.services.capacity import get_global_sold_count
 from django_program.settings import get_config
 from django_program.sponsors.models import Sponsor, SponsorLevel
 from django_program.sponsors.profiles.resolver import resolve_sponsor_profile
@@ -2410,9 +2411,12 @@ class TicketTypeListView(ManagePermissionMixin, ListView):
     paginate_by = 50
 
     def get_context_data(self, **kwargs: object) -> dict[str, object]:
-        """Add ``active_nav`` to the template context."""
+        """Add ``active_nav`` and global capacity info to the template context."""
         context = super().get_context_data(**kwargs)
         context["active_nav"] = "ticket-types"
+        if self.conference.total_capacity > 0:
+            context["global_capacity"] = self.conference.total_capacity
+            context["global_sold"] = get_global_sold_count(self.conference)
         return context
 
     def get_queryset(self) -> QuerySet[TicketType]:
diff --git a/src/django_program/registration/services/capacity.py b/src/django_program/registration/services/capacity.py
new file mode 100644
index 0000000..78eb2bc
--- /dev/null
+++ b/src/django_program/registration/services/capacity.py
@@ -0,0 +1,94 @@
+"""Global ticket capacity enforcement for conferences.
+
+Provides functions to count, check, and validate total ticket sales against
+a conference-level capacity limit. Add-ons are excluded from the global count
+because they do not consume venue seats.
+"""
+
+from django.core.exceptions import ValidationError
+from django.db import models
+from django.utils import timezone
+
+from django_program.conference.models import Conference
+from django_program.registration.models import Order, OrderLineItem
+
+
+def get_global_sold_count(conference: object) -> int:
+    """Return the total number of tickets sold across all ticket types.
+
+    Counts OrderLineItem quantities for ticket-type items (not add-ons) in
+    orders that are PAID, PARTIALLY_REFUNDED, or PENDING with an active
+    inventory hold.
+
+    Uses ``addon__isnull=True`` rather than ``ticket_type__isnull=False`` so
+    that line items whose ticket type was deleted (SET_NULL) are still counted
+    toward the sold total, preventing oversells.
+
+    Args:
+        conference: The conference to count sales for.
+
+    Returns:
+        The total number of tickets sold.
+    """
+    now = timezone.now()
+    return (
+        OrderLineItem.objects.filter(
+            order__conference=conference,
+            addon__isnull=True,
+        )
+        .filter(
+            models.Q(order__status__in=[Order.Status.PAID, Order.Status.PARTIALLY_REFUNDED])
+            | models.Q(order__status=Order.Status.PENDING, order__hold_expires_at__gt=now),
+        )
+        .aggregate(total=models.Sum("quantity"))["total"]
+        or 0
+    )
+
+
+def get_global_remaining(conference: object) -> int | None:
+    """Return the number of tickets still available under the global cap.
+
+    Args:
+        conference: The conference to check capacity for.
+
+    Returns:
+        The remaining ticket count, or ``None`` if the conference has no
+        global capacity limit (``total_capacity == 0``).
+    """
+    if conference.total_capacity == 0:
+        return None
+    sold = get_global_sold_count(conference)
+    return conference.total_capacity - sold
+
+
+def validate_global_capacity(conference: object, desired_total: int) -> None:
+    """Raise ``ValidationError`` if ``desired_total`` would exceed global capacity.
+
+    Acquires a row-level lock on the conference via ``select_for_update()`` to
+    prevent race conditions when multiple concurrent requests validate capacity
+    at the same time. The caller **must** already be inside a
+    ``transaction.atomic`` block.
+
+    The early-return check for unlimited conferences happens **after** the lock
+    is acquired so that a stale in-memory instance cannot bypass enforcement.
+
+    Args:
+        conference: The conference to validate against.
+        desired_total: The total number of ticket items in the cart
+            (across all ticket types, excluding add-ons).
+
+    Raises:
+        ValidationError: If the desired total exceeds the conference's
+            ``total_capacity``.
+    """
+    locked = Conference.objects.select_for_update().get(pk=conference.pk)
+    if locked.total_capacity == 0:
+        return
+    sold = get_global_sold_count(locked)
+    remaining = locked.total_capacity - sold
+    if desired_total > remaining:
+        if remaining <= 0:
+            raise ValidationError(f"This conference is sold out (venue capacity: {locked.total_capacity}).")
+        raise ValidationError(
+            f"Only {remaining} tickets remaining for this conference (venue capacity: {locked.total_capacity})."
+        )
diff --git a/src/django_program/registration/services/cart.py b/src/django_program/registration/services/cart.py
index a5baeb3..6a97be8 100644
--- a/src/django_program/registration/services/cart.py
+++ b/src/django_program/registration/services/cart.py
@@ -22,6 +22,7 @@
     TicketType,
     Voucher,
 )
+from django_program.registration.services.capacity import validate_global_capacity
 from django_program.settings import get_config
 
 
@@ -131,6 +132,11 @@ def add_ticket(cart: Cart, ticket_type: TicketType, qty: int = 1) -> CartItem:
         existing_in_orders=existing_in_orders,
     )
 
+    validate_global_capacity(
+        cart.conference,
+        _get_cart_total_ticket_qty(cart) + qty,
+    )
+
     if ticket_type.requires_voucher:
         voucher = cart.voucher
         if voucher is None or not voucher.unlocks_hidden_tickets:
@@ -666,6 +672,9 @@ def _validate_ticket_quantity(cart: Cart, ticket_type: TicketType, new_qty: int)
             f"{ticket_type.limit_per_user} for '{ticket_type.name}'."
         )
 
+    other_ticket_qty = _get_cart_total_ticket_qty(cart, exclude_ticket_type=ticket_type)
+    validate_global_capacity(cart.conference, other_ticket_qty + new_qty)
+
 
 def _validate_addon_quantity(addon: AddOn, new_qty: int) -> None:
     """Validate remaining stock for a new add-on quantity."""
@@ -708,6 +717,24 @@ def _cascade_remove_orphaned_addons(cart: Cart, removing_ticket_type_id: int) ->
             addon_item.delete()
 
 
+def _get_cart_total_ticket_qty(cart: Cart, *, exclude_ticket_type: TicketType | None = None) -> int:
+    """Return the total ticket quantity in the cart (excluding add-ons).
+
+    Args:
+        cart: The cart to sum ticket items from.
+        exclude_ticket_type: Optionally exclude items of this ticket type
+            from the sum (used by ``update_quantity`` to compute the total
+            of *other* tickets before adding the new quantity).
+
+    Returns:
+        The total number of ticket items in the cart.
+    """
+    qs = cart.items.filter(ticket_type__isnull=False)
+    if exclude_ticket_type is not None:
+        qs = qs.exclude(ticket_type=exclude_ticket_type)
+    return qs.aggregate(total=models.Sum("quantity"))["total"] or 0
+
+
 def _item_is_voucher_applicable(
     item: CartItem,
     applicable_ticket_ids: set[int] | None,
diff --git a/src/django_program/registration/services/checkout.py b/src/django_program/registration/services/checkout.py
index b81c103..2b95f01 100644
--- a/src/django_program/registration/services/checkout.py
+++ b/src/django_program/registration/services/checkout.py
@@ -22,6 +22,7 @@
     Payment,
     Voucher,
 )
+from django_program.registration.services.capacity import validate_global_capacity
 from django_program.registration.services.cart import get_summary_from_items
 from django_program.registration.signals import order_paid
 from django_program.settings import get_config
@@ -100,7 +101,7 @@ def checkout(
         if not items:
             raise ValidationError("Cannot check out an empty cart.")
 
-        _revalidate_stock(items)
+        _revalidate_stock(items, cart.conference)
 
         summary = get_summary_from_items(cart, items)
 
@@ -339,9 +340,13 @@ def _increment_voucher_usage(*, voucher: Voucher | None, now: object) -> None:
         raise ValidationError(f"Voucher code '{voucher.code}' is no longer valid.")
 
 
-def _revalidate_stock(items: list[object]) -> None:
+def _revalidate_stock(items: list[object], conference: object) -> None:
     """Re-validate stock availability for all cart items at checkout time.
 
+    Args:
+        items: Pre-fetched cart items to validate.
+        conference: The conference these items belong to.
+
     Raises:
         ValidationError: If any item has insufficient stock or missing prerequisites.
     """
@@ -353,6 +358,28 @@ def _revalidate_stock(items: list[object]) -> None:
         elif item.addon is not None:
             _revalidate_addon_stock(item, now, ticket_type_ids)
 
+    _revalidate_global_capacity(items, conference)
+
+
+def _revalidate_global_capacity(items: list[object], conference: object) -> None:
+    """Validate that checkout ticket quantities fit within the global cap.
+
+    Sums ticket quantities from the cart items and validates against the
+    conference's ``total_capacity``.
+
+    Args:
+        items: Pre-fetched cart items from the checkout flow.
+        conference: The conference to validate capacity against.
+
+    Raises:
+        ValidationError: If the total tickets would exceed the global cap.
+    """
+    ticket_items = [item for item in items if item.ticket_type_id is not None]
+    if not ticket_items:
+        return
+    total_qty = sum(item.quantity for item in ticket_items)
+    validate_global_capacity(conference, total_qty)
+
 
 def _revalidate_ticket_stock(item: object) -> None:
     """Validate a ticket type is still available with sufficient stock."""
diff --git a/tests/test_conference/test_bootstrap_command.py b/tests/test_conference/test_bootstrap_command.py
index d7b5a37..15cc72e 100644
--- a/tests/test_conference/test_bootstrap_command.py
+++ b/tests/test_conference/test_bootstrap_command.py
@@ -448,3 +448,50 @@ def test_bootstrap_deferred_keys_prints_notice(tmp_path):
 
     assert "Skipping 'sponsor_levels'" in output
     assert "sponsors app" in output
+
+
+@pytest.mark.django_db
+def test_bootstrap_sets_total_capacity(tmp_path):
+    config_path = _write_config(
+        tmp_path / "capacity.toml",
+        """[conference]
+name = "PyCon Capacity Test"
+start = 2027-05-01
+end = 2027-05-03
+timezone = "UTC"
+total_capacity = 1000
+
+[[conference.sections]]
+name = "Talks"
+start = 2027-05-02
+end = 2027-05-02
+""",
+    )
+
+    call_command("bootstrap_conference", config=config_path)
+
+    conference = Conference.objects.get(slug="pycon-capacity-test")
+    assert conference.total_capacity == 1000
+
+
+@pytest.mark.django_db
+def test_bootstrap_without_total_capacity_defaults_to_zero(tmp_path):
+    config_path = _write_config(
+        tmp_path / "no_capacity.toml",
+        """[conference]
+name = "PyCon No Cap"
+start = 2027-05-01
+end = 2027-05-03
+timezone = "UTC"
+
+[[conference.sections]]
+name = "Talks"
+start = 2027-05-02
+end = 2027-05-02
+""",
+    )
+
+    call_command("bootstrap_conference", config=config_path)
+
+    conference = Conference.objects.get(slug="pycon-no-cap")
+    assert conference.total_capacity == 0
diff --git a/tests/test_manage/test_forms.py b/tests/test_manage/test_forms.py
index bcf40b6..f3bfdb2 100644
--- a/tests/test_manage/test_forms.py
+++ b/tests/test_manage/test_forms.py
@@ -63,6 +63,7 @@ def test_meta_fields(self):
             "address",
             "website_url",
             "pretalx_event_slug",
+            "total_capacity",
             "is_active",
         ]
         assert list(form.fields.keys()) == expected
@@ -74,6 +75,7 @@ def test_valid_data(self):
                 "start_date": "2027-05-01",
                 "end_date": "2027-05-03",
                 "timezone": "UTC",
+                "total_capacity": 0,
                 "is_active": True,
             }
         )
diff --git a/tests/test_manage/test_programs_views.py b/tests/test_manage/test_programs_views.py
index eb9ca12..5bc6bb9 100644
--- a/tests/test_manage/test_programs_views.py
+++ b/tests/test_manage/test_programs_views.py
@@ -710,6 +710,14 @@ def test_activity_promote_non_waitlisted_404(authed_client: Client, conference,
     assert response.status_code == 404
 
 
+@pytest.mark.django_db
+def test_activity_dashboard_redirects_unauthenticated_user(client: Client, conference, activity):
+    url = reverse("manage:activity-dashboard", kwargs={"conference_slug": conference.slug, "pk": activity.pk})
+    response = client.get(url)
+    assert response.status_code == 302
+    assert "/accounts/login/" in response.url
+
+
 # ---- Activity organizers M2M ----
 
 
diff --git a/tests/test_manage/test_views.py b/tests/test_manage/test_views.py
index 6717970..62fc76a 100644
--- a/tests/test_manage/test_views.py
+++ b/tests/test_manage/test_views.py
@@ -400,6 +400,7 @@ def test_post_valid_form(self, client_logged_in_super, conference):
                 "start_date": "2027-05-01",
                 "end_date": "2027-05-03",
                 "timezone": "UTC",
+                "total_capacity": 0,
                 "is_active": "on",
             },
         )
@@ -416,6 +417,7 @@ def test_get_success_url_redirects_to_dashboard(self, client_logged_in_super, co
                 "start_date": "2027-05-01",
                 "end_date": "2027-05-03",
                 "timezone": "UTC",
+                "total_capacity": 0,
                 "is_active": "on",
             },
         )
@@ -2070,6 +2072,29 @@ def test_ticket_type_edit_success_url(self, client_logged_in_super, conference,
         expected = reverse("manage:ticket-type-list", kwargs={"conference_slug": conference.slug})
         assert resp.url == expected
 
+    def test_ticket_type_list_includes_global_capacity(self, client_logged_in_super, db):
+        """When total_capacity > 0, context includes capacity info."""
+        capped = Conference.objects.create(
+            name="CappedCon",
+            slug="cappedcon-views",
+            start_date=date(2027, 6, 1),
+            end_date=date(2027, 6, 3),
+            total_capacity=100,
+        )
+        url = reverse("manage:ticket-type-list", kwargs={"conference_slug": capped.slug})
+        resp = client_logged_in_super.get(url)
+        assert resp.status_code == 200
+        assert resp.context["global_capacity"] == 100
+        assert resp.context["global_sold"] == 0
+
+    def test_ticket_type_list_excludes_global_capacity_when_zero(self, client_logged_in_super, conference):
+        """When total_capacity is 0, context does not include capacity info."""
+        url = reverse("manage:ticket-type-list", kwargs={"conference_slug": conference.slug})
+        resp = client_logged_in_super.get(url)
+        assert resp.status_code == 200
+        assert "global_capacity" not in resp.context
+        assert "global_sold" not in resp.context
+
 
 # ---------------------------------------------------------------------------
 # _unique_ticket_type_slug
diff --git a/tests/test_registration/test_capacity.py b/tests/test_registration/test_capacity.py
new file mode 100644
index 0000000..82cc6e8
--- /dev/null
+++ b/tests/test_registration/test_capacity.py
@@ -0,0 +1,342 @@
+"""Tests for global capacity enforcement in django_program.registration.services.capacity."""
+
+from datetime import date, timedelta
+from decimal import Decimal
+from uuid import uuid4
+
+import pytest
+from django.contrib.auth import get_user_model
+from django.core.exceptions import ValidationError
+from django.utils import timezone
+
+from django_program.conference.models import Conference
+from django_program.registration.models import (
+    AddOn,
+    Order,
+    OrderLineItem,
+    TicketType,
+)
+from django_program.registration.services.capacity import (
+    get_global_remaining,
+    get_global_sold_count,
+    validate_global_capacity,
+)
+
+User = get_user_model()
+
+
+def _make_order(*, conference, user, status, reference=None, hold_expires_at=None):
+    kwargs = {
+        "conference": conference,
+        "user": user,
+        "status": status,
+        "subtotal": Decimal("0.00"),
+        "total": Decimal("0.00"),
+        "reference": reference or f"ORD-{uuid4().hex[:8].upper()}",
+    }
+    if hold_expires_at is not None:
+        kwargs["hold_expires_at"] = hold_expires_at
+    return Order.objects.create(**kwargs)
+
+
+@pytest.fixture
+def conference():
+    return Conference.objects.create(
+        name="CapCon",
+        slug="capcon",
+        start_date=date(2027, 6, 1),
+        end_date=date(2027, 6, 3),
+        timezone="UTC",
+        total_capacity=10,
+    )
+
+
+@pytest.fixture
+def unlimited_conference():
+    return Conference.objects.create(
+        name="UnlimitedCon",
+        slug="unlimitedcon",
+        start_date=date(2027, 7, 1),
+        end_date=date(2027, 7, 3),
+        timezone="UTC",
+        total_capacity=0,
+    )
+
+
+@pytest.fixture
+def user():
+    return User.objects.create_user(
+        username="capuser",
+        email="cap@example.com",
+        password="testpass123",
+    )
+
+
+@pytest.fixture
+def ticket_type(conference):
+    return TicketType.objects.create(
+        conference=conference,
+        name="General",
+        slug="general",
+        price=Decimal("100.00"),
+        total_quantity=0,
+        limit_per_user=10,
+        is_active=True,
+    )
+
+
+@pytest.fixture
+def addon(conference):
+    return AddOn.objects.create(
+        conference=conference,
+        name="T-Shirt",
+        slug="tshirt",
+        price=Decimal("25.00"),
+        total_quantity=0,
+        is_active=True,
+    )
+
+
+@pytest.mark.django_db
+class TestGetGlobalSoldCount:
+    def test_empty_conference_returns_zero(self, conference):
+        assert get_global_sold_count(conference) == 0
+
+    def test_counts_paid_orders(self, conference, user, ticket_type):
+        order = _make_order(conference=conference, user=user, status=Order.Status.PAID)
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ticket",
+            quantity=3,
+            unit_price=Decimal("100.00"),
+            line_total=Decimal("300.00"),
+            ticket_type=ticket_type,
+        )
+        assert get_global_sold_count(conference) == 3
+
+    def test_counts_partially_refunded(self, conference, user, ticket_type):
+        order = _make_order(conference=conference, user=user, status=Order.Status.PARTIALLY_REFUNDED)
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ticket",
+            quantity=2,
+            unit_price=Decimal("100.00"),
+            line_total=Decimal("200.00"),
+            ticket_type=ticket_type,
+        )
+        assert get_global_sold_count(conference) == 2
+
+    def test_counts_pending_with_active_hold(self, conference, user, ticket_type):
+        future = timezone.now() + timedelta(minutes=30)
+        order = _make_order(
+            conference=conference,
+            user=user,
+            status=Order.Status.PENDING,
+            hold_expires_at=future,
+        )
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ticket",
+            quantity=1,
+            unit_price=Decimal("100.00"),
+            line_total=Decimal("100.00"),
+            ticket_type=ticket_type,
+        )
+        assert get_global_sold_count(conference) == 1
+
+    def test_ignores_pending_with_expired_hold(self, conference, user, ticket_type):
+        past = timezone.now() - timedelta(minutes=30)
+        order = _make_order(
+            conference=conference,
+            user=user,
+            status=Order.Status.PENDING,
+            hold_expires_at=past,
+        )
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ticket",
+            quantity=5,
+            unit_price=Decimal("100.00"),
+            line_total=Decimal("500.00"),
+            ticket_type=ticket_type,
+        )
+        assert get_global_sold_count(conference) == 0
+
+    def test_ignores_cancelled_orders(self, conference, user, ticket_type):
+        order = _make_order(conference=conference, user=user, status=Order.Status.CANCELLED)
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ticket",
+            quantity=4,
+            unit_price=Decimal("100.00"),
+            line_total=Decimal("400.00"),
+            ticket_type=ticket_type,
+        )
+        assert get_global_sold_count(conference) == 0
+
+    def test_ignores_refunded_orders(self, conference, user, ticket_type):
+        order = _make_order(conference=conference, user=user, status=Order.Status.REFUNDED)
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ticket",
+            quantity=4,
+            unit_price=Decimal("100.00"),
+            line_total=Decimal("400.00"),
+            ticket_type=ticket_type,
+        )
+        assert get_global_sold_count(conference) == 0
+
+    def test_excludes_addons(self, conference, user, addon):
+        order = _make_order(conference=conference, user=user, status=Order.Status.PAID)
+        OrderLineItem.objects.create(
+            order=order,
+            description="T-Shirt",
+            quantity=10,
+            unit_price=Decimal("25.00"),
+            line_total=Decimal("250.00"),
+            addon=addon,
+        )
+        assert get_global_sold_count(conference) == 0
+
+    def test_sums_across_ticket_types(self, conference, user):
+        tt_a = TicketType.objects.create(
+            conference=conference,
+            name="A",
+            slug="a",
+            price=Decimal("50.00"),
+            total_quantity=0,
+            limit_per_user=10,
+            is_active=True,
+        )
+        tt_b = TicketType.objects.create(
+            conference=conference,
+            name="B",
+            slug="b",
+            price=Decimal("75.00"),
+            total_quantity=0,
+            limit_per_user=10,
+            is_active=True,
+        )
+        order = _make_order(conference=conference, user=user, status=Order.Status.PAID)
+        OrderLineItem.objects.create(
+            order=order,
+            description="A",
+            quantity=3,
+            unit_price=Decimal("50.00"),
+            line_total=Decimal("150.00"),
+            ticket_type=tt_a,
+        )
+        OrderLineItem.objects.create(
+            order=order,
+            description="B",
+            quantity=4,
+            unit_price=Decimal("75.00"),
+            line_total=Decimal("300.00"),
+            ticket_type=tt_b,
+        )
+        assert get_global_sold_count(conference) == 7
+
+    def test_counts_orphaned_line_items_after_ticket_type_deleted(self, conference, user):
+        """Line items whose ticket_type was deleted (SET_NULL) must still count."""
+        tt = TicketType.objects.create(
+            conference=conference,
+            name="Ephemeral",
+            slug="ephemeral",
+            price=Decimal("50.00"),
+            total_quantity=0,
+            limit_per_user=10,
+            is_active=True,
+        )
+        order = _make_order(conference=conference, user=user, status=Order.Status.PAID)
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ephemeral",
+            quantity=4,
+            unit_price=Decimal("50.00"),
+            line_total=Decimal("200.00"),
+            ticket_type=tt,
+        )
+        assert get_global_sold_count(conference) == 4
+        tt.delete()
+        assert get_global_sold_count(conference) == 4
+
+
+@pytest.mark.django_db
+class TestGetGlobalRemaining:
+    def test_no_limit_returns_none(self, unlimited_conference):
+        assert get_global_remaining(unlimited_conference) is None
+
+    def test_returns_remaining_when_limit_set(self, conference, user, ticket_type):
+        order = _make_order(conference=conference, user=user, status=Order.Status.PAID)
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ticket",
+            quantity=3,
+            unit_price=Decimal("100.00"),
+            line_total=Decimal("300.00"),
+            ticket_type=ticket_type,
+        )
+        assert get_global_remaining(conference) == 7  # 10 - 3
+
+    def test_empty_conference_returns_full_capacity(self, conference):
+        assert get_global_remaining(conference) == 10
+
+
+@pytest.mark.django_db
+class TestValidateGlobalCapacity:
+    def test_no_limit_bypasses_validation(self, unlimited_conference):
+        validate_global_capacity(unlimited_conference, 99999)
+
+    def test_under_capacity_passes(self, conference):
+        validate_global_capacity(conference, 5)
+
+    def test_at_capacity_passes(self, conference):
+        validate_global_capacity(conference, 10)
+
+    def test_over_capacity_raises(self, conference):
+        with pytest.raises(ValidationError, match="Only 10 tickets remaining"):
+            validate_global_capacity(conference, 11)
+
+    def test_over_capacity_with_existing_sales(self, conference, user, ticket_type):
+        order = _make_order(conference=conference, user=user, status=Order.Status.PAID)
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ticket",
+            quantity=8,
+            unit_price=Decimal("100.00"),
+            line_total=Decimal("800.00"),
+            ticket_type=ticket_type,
+        )
+        validate_global_capacity(conference, 2)  # 8 sold + 2 new = 10
+
+        with pytest.raises(ValidationError, match="Only 2 tickets remaining"):
+            validate_global_capacity(conference, 3)
+
+    def test_sold_out_message_when_at_capacity(self, conference, user, ticket_type):
+        """When remaining is exactly 0, the error should say 'sold out'."""
+        order = _make_order(conference=conference, user=user, status=Order.Status.PAID)
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ticket",
+            quantity=10,
+            unit_price=Decimal("100.00"),
+            line_total=Decimal("1000.00"),
+            ticket_type=ticket_type,
+        )
+        with pytest.raises(ValidationError, match="sold out"):
+            validate_global_capacity(conference, 1)
+
+    def test_sold_out_message_when_oversold(self, conference, user, ticket_type):
+        """When capacity is lowered below current sales, the error should say 'sold out'."""
+        order = _make_order(conference=conference, user=user, status=Order.Status.PAID)
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ticket",
+            quantity=12,
+            unit_price=Decimal("100.00"),
+            line_total=Decimal("1200.00"),
+            ticket_type=ticket_type,
+        )
+        # remaining is negative (-2), should show "sold out" not "-2 tickets remaining"
+        with pytest.raises(ValidationError, match="sold out"):
+            validate_global_capacity(conference, 1)
diff --git a/tests/test_registration/test_cart_service.py b/tests/test_registration/test_cart_service.py
index 97d15f7..6fdf2ba 100644
--- a/tests/test_registration/test_cart_service.py
+++ b/tests/test_registration/test_cart_service.py
@@ -1297,3 +1297,98 @@ def test_apply_voucher_discounts_unknown_type(self, cart, ticket_type, conferenc
         )
         result = _apply_voucher_discounts(voucher, [line], [(0, Decimal("100.00"))])
         assert result == Decimal("0.00")
+
+
+# =============================================================================
+# TestGlobalCapacityCartIntegration
+# =============================================================================
+
+
+@pytest.mark.django_db
+class TestGlobalCapacityCartIntegration:
+    """Tests that add_ticket and update_quantity enforce global capacity."""
+
+    @pytest.fixture
+    def capped_conference(self):
+        return Conference.objects.create(
+            name="CappedCon",
+            slug="cappedcon-cart",
+            start_date=date(2027, 6, 1),
+            end_date=date(2027, 6, 3),
+            timezone="UTC",
+            total_capacity=5,
+        )
+
+    @pytest.fixture
+    def capped_ticket(self, capped_conference):
+        return TicketType.objects.create(
+            conference=capped_conference,
+            name="General",
+            slug="general",
+            price=Decimal("100.00"),
+            total_quantity=0,
+            limit_per_user=10,
+            is_active=True,
+        )
+
+    @pytest.fixture
+    def capped_cart(self, capped_conference, user):
+        return Cart.objects.create(
+            user=user,
+            conference=capped_conference,
+            status=Cart.Status.OPEN,
+            expires_at=timezone.now() + timedelta(minutes=30),
+        )
+
+    def test_add_ticket_respects_global_cap(self, capped_cart, capped_ticket):
+        add_ticket(capped_cart, capped_ticket, qty=5)
+
+        with pytest.raises(ValidationError, match="tickets remaining for this conference"):
+            add_ticket(capped_cart, capped_ticket, qty=1)
+
+    def test_add_ticket_bypasses_when_no_cap(self, cart, ticket_type):
+        # conference fixture has total_capacity=0 (default, no limit)
+        add_ticket(cart, ticket_type, qty=10)
+        assert cart.items.first().quantity == 10
+
+    def test_update_quantity_respects_global_cap(self, capped_cart, capped_ticket):
+        item = add_ticket(capped_cart, capped_ticket, qty=3)
+
+        with pytest.raises(ValidationError, match="tickets remaining for this conference"):
+            update_quantity(capped_cart, item.pk, 6)
+
+    def test_update_quantity_within_cap_succeeds(self, capped_cart, capped_ticket):
+        item = add_ticket(capped_cart, capped_ticket, qty=3)
+        result = update_quantity(capped_cart, item.pk, 5)
+        assert result.quantity == 5
+
+    def test_global_cap_with_multiple_ticket_types(self, capped_conference, user):
+        tt_a = TicketType.objects.create(
+            conference=capped_conference,
+            name="A",
+            slug="a",
+            price=Decimal("50.00"),
+            total_quantity=0,
+            limit_per_user=10,
+            is_active=True,
+        )
+        tt_b = TicketType.objects.create(
+            conference=capped_conference,
+            name="B",
+            slug="b",
+            price=Decimal("75.00"),
+            total_quantity=0,
+            limit_per_user=10,
+            is_active=True,
+        )
+        cart = Cart.objects.create(
+            user=user,
+            conference=capped_conference,
+            status=Cart.Status.OPEN,
+            expires_at=timezone.now() + timedelta(minutes=30),
+        )
+        add_ticket(cart, tt_a, qty=3)
+        add_ticket(cart, tt_b, qty=2)  # total = 5 = cap
+
+        with pytest.raises(ValidationError, match="tickets remaining for this conference"):
+            add_ticket(cart, tt_a, qty=1)
diff --git a/tests/test_registration/test_checkout_service.py b/tests/test_registration/test_checkout_service.py
index 452b331..128d770 100644
--- a/tests/test_registration/test_checkout_service.py
+++ b/tests/test_registration/test_checkout_service.py
@@ -34,6 +34,7 @@
     CheckoutService,
     _expire_stale_pending_orders,
     _increment_voucher_usage,
+    _revalidate_global_capacity,
 )
 from django_program.registration.signals import order_paid
 
@@ -1056,3 +1057,107 @@ def test_expire_decrements_voucher_usage(self, conference, user):
 
         voucher.refresh_from_db()
         assert voucher.times_used == 2
+
+
+# =============================================================================
+# TestGlobalCapacityCheckoutIntegration
+# =============================================================================
+
+
+@pytest.mark.django_db
+class TestGlobalCapacityCheckoutIntegration:
+    """Tests that checkout revalidation enforces global capacity."""
+
+    @pytest.fixture
+    def capped_conference(self):
+        return Conference.objects.create(
+            name="CappedCheckout",
+            slug="capped-checkout",
+            start_date=date(2027, 6, 1),
+            end_date=date(2027, 6, 3),
+            timezone="UTC",
+            total_capacity=3,
+        )
+
+    @pytest.fixture
+    def capped_ticket(self, capped_conference):
+        return TicketType.objects.create(
+            conference=capped_conference,
+            name="General",
+            slug="general",
+            price=Decimal("100.00"),
+            total_quantity=0,
+            limit_per_user=10,
+            is_active=True,
+        )
+
+    @pytest.fixture
+    def capped_cart_with_ticket(self, capped_conference, user, capped_ticket):
+        cart = Cart.objects.create(
+            user=user,
+            conference=capped_conference,
+            status=Cart.Status.OPEN,
+            expires_at=timezone.now() + timedelta(minutes=30),
+        )
+        add_ticket(cart, capped_ticket, qty=2)
+        return cart
+
+    def test_checkout_passes_within_global_cap(self, capped_cart_with_ticket):
+        order = CheckoutService.checkout(capped_cart_with_ticket)
+        assert order.status == Order.Status.PENDING
+
+    def test_checkout_revalidation_catches_oversell(self, capped_conference, user, capped_ticket):
+        """Simulate oversell: another user buys tickets between cart-add and checkout."""
+        cart = Cart.objects.create(
+            user=user,
+            conference=capped_conference,
+            status=Cart.Status.OPEN,
+            expires_at=timezone.now() + timedelta(minutes=30),
+        )
+        add_ticket(cart, capped_ticket, qty=2)
+
+        # Another user buys 2 tickets (total sold = 2, cap = 3)
+        other_user = User.objects.create_user(
+            username="oversell-other",
+            email="oversell@example.com",
+            password="testpass123",
+        )
+        order = Order.objects.create(
+            conference=capped_conference,
+            user=other_user,
+            status=Order.Status.PAID,
+            subtotal=Decimal("200.00"),
+            total=Decimal("200.00"),
+            reference=f"ORD-{uuid4().hex[:8].upper()}",
+        )
+        OrderLineItem.objects.create(
+            order=order,
+            description="Ticket",
+            quantity=2,
+            unit_price=Decimal("100.00"),
+            line_total=Decimal("200.00"),
+            ticket_type=capped_ticket,
+        )
+
+        # Now user tries to check out 2 more (total would be 4 > cap 3)
+        with pytest.raises(ValidationError, match="tickets remaining for this conference"):
+            CheckoutService.checkout(cart)
+
+    def test_revalidate_global_capacity_skips_addon_only_items(self, capped_conference):
+        """When all cart items are add-ons (no ticket_type_id), skip capacity check."""
+        addon = AddOn.objects.create(
+            conference=capped_conference,
+            name="Swag",
+            slug="swag-cap",
+            price=Decimal("15.00"),
+            is_active=True,
+        )
+        cart = Cart.objects.create(
+            user=User.objects.create_user(username="addon-only", password="testpass123"),
+            conference=capped_conference,
+            status=Cart.Status.OPEN,
+            expires_at=timezone.now() + timedelta(minutes=30),
+        )
+        add_addon(cart, addon, qty=1)
+        items = list(cart.items.select_related("ticket_type", "addon"))
+        _revalidate_global_capacity(items, capped_conference)