diff --git a/Makefile b/Makefile
index 946533a..4760b9b 100644
--- a/Makefile
+++ b/Makefile
@@ -8,7 +8,7 @@ include platform/helm/versions.env
 export
 
 .DEFAULT_GOAL := help
-.PHONY: help bootstrap validate scan up status port-forward rollback down
+.PHONY: help bootstrap validate scan up status port-forward rollback down argocd-bootstrap argocd-status argocd-port-forward argocd-down
 
 help: ## Show available commands.
 	@grep -E '^[a-zA-Z_-]+:.*?## ' $(MAKEFILE_LIST) | awk 'BEGIN {FS = ":.*?## "}; {printf "%-16s %s\n", $$1, $$2}'
@@ -46,3 +46,28 @@ rollback: ## Roll back the release by one revision after checking Helm history.
 
 down: ## Delete the complete local cluster and all of its resources.
 	kind delete cluster --name $(CLUSTER_NAME)
+
+argocd-bootstrap: ## Install Argo CD, wait for rollout, and deploy the application.
+	./platform/argocd/install-argocd.sh
+
+argocd-status: ## Display Argo CD application status and target workloads.
+	@echo "=== Argo CD Application Status ==="
+	kubectl get application astronomy-shop -n argocd -o wide || echo "Argo CD Application not found."
+	@echo "=== Workload Status ==="
+	kubectl get pods -n $(NAMESPACE)
+
+argocd-port-forward: ## Expose Argo CD UI (https://localhost:8082) and storefront (http://localhost:8080).
+	@echo "Argo CD UI:  https://localhost:8082"
+	@echo "Storefront:  http://localhost:8080"
+	@echo "Retrieving Argo CD admin password..."
+	@kubectl -n argocd get secret argocd-initial-admin-secret -o jsonpath="{.data.password}" | base64 -d; echo
+	# Run port-forwards (Ctrl+C to terminate)
+	kubectl port-forward svc/argocd-server -n argocd 8082:443 & \
+	kubectl port-forward svc/$(RELEASE_NAME)-frontendproxy -n $(NAMESPACE) 8080:8080 & \
+	wait
+
+argocd-down: ## Delete Argo CD application and namespaces.
+	kubectl delete -f platform/argocd/application.yaml --ignore-not-found=true
+	kubectl delete namespace $(NAMESPACE) --ignore-not-found=true
+	kubectl delete namespace argocd --ignore-not-found=true
+
diff --git a/docs/adr/0004-gitops-and-cd-strategy.md b/docs/adr/0004-gitops-and-cd-strategy.md
new file mode 100644
index 0000000..8532512
--- /dev/null
+++ b/docs/adr/0004-gitops-and-cd-strategy.md
@@ -0,0 +1,45 @@
+# 4. GitOps and Continuous Delivery Strategy
+
+Date: 2026-07-20
+
+## Status
+
+Accepted
+
+## Context
+
+We need to establish a Continuous Delivery (CD) mechanism that aligns with GitOps principles. Rather than relying on manual scripts (`make up`) or push-based pipelines to apply changes directly to our Kubernetes cluster, the cluster state should be driven declaratively by the configurations stored in this Git repository. 
+
+Our microservices application (Astronomy Shop) has 15+ services, making it crucial to have:
+1. Automated sync policies to ensure the cluster matches Git configuration.
+2. Drift detection and self-healing to automatically revert manual `kubectl` overrides.
+3. High visibility into the deployment state, dependencies, and health of each microservice.
+
+We evaluated two major CNCF GitOps tools: **Argo CD** and **Flux CD**.
+
+### Argo CD vs. Flux CD Comparison
+
+| Feature | Argo CD | Flux CD |
+|---|---|---|
+| **Architecture** | Centralized API Server & Controller (Pull-based) | Modular controllers (Source, Helm, Kustomize) |
+| **User Interface** | Rich, interactive web UI out-of-the-box | CLI-first; requires third-party UI (e.g., Weave GitOps) |
+| **Application Model** | Single CRD (`Application` / `ApplicationSet`) | Decoupled CRDs (`GitRepository`, `HelmRelease`) |
+| **Multiple Sources** | Supported natively (v2.6+); simple configuration | Supported natively by decoupling sources and releases |
+| **Visualization** | Excellent visualization of resource dependency trees | Minimal representation without third-party addons |
+| **Reconciliation** | Instant webhook or periodic poll (default 3m) | Periodic reconciliation based on configured intervals |
+
+## Decision
+
+We will use **Argo CD** as our GitOps and CD engine for the local DevSecOps platform.
+
+1.  **Multiple Sources Engine:** We will utilize Argo CD's Multiple Sources feature to point to the upstream Helm repository for the Astronomy Shop chart (`opentelemetry-demo`) while sourcing our custom configuration (`values.yaml`) directly from this Git repository. This avoids duplications and wrapper chart maintenance.
+2.  **Automated Reconciliation:** We will enable automatic pruning (removing deleted resources) and self-healing (reverting manual cluster drift).
+3.  **Visualization:** The Argo CD Web UI will be exposed via a port-forwarding target to provide developer-friendly visibility into the complex microservice landscape.
+
+## Consequences
+
+*   **Positive:** Single source of truth for the entire platform state. Manual changes to the cluster are automatically corrected.
+*   **Positive:** Highly visual representation of the application structure, helping developers understand microservice dependencies.
+*   **Positive:** No duplicate Helm values or complex umbrella charts required to use GitOps with upstream dependencies.
+*   **Negative:** Increased local cluster footprint. Argo CD running controllers, Redis, and its API server will consume ~500MiB–1GiB of memory.
+*   **Negative:** Requires managing Git access credentials in a production environment (not applicable here as we use a public repository and local cluster).
diff --git a/docs/journey.md b/docs/journey.md
index 253aea8..a8809ef 100644
--- a/docs/journey.md
+++ b/docs/journey.md
@@ -95,12 +95,24 @@ pip
 
 ---
 
-## Next Objective
+## 2026-07-20
+
+### GitOps with Argo CD
+
+Completed:
+
+* Evaluated GitOps tools (Argo CD vs Flux CD) and detailed choices in ADR-0004.
+* Created declarative installer `platform/argocd/install-argocd.sh` to configure the namespace, pull stable manifests, wait for rollout, and bootstrap application.
+* Implemented multiple-source `platform/argocd/application.yaml` linking the official OpenTelemetry demo Helm repository to our local values file configuration.
+* Added `argocd-*` targets to Makefile for easy lifecycle management.
 
-Push the CI refactor.
+Lesson learned:
+
+Using Argo CD's Multiple Sources feature is a powerful way to reference upstream Helm charts while maintaining custom value overrides in a separate Git repository, keeping the codebase clean and eliminating local wrapper charts.
 
-Review GitHub Actions.
+---
+
+## Next Objective
 
-Fix failures.
+Push the `feature/phase4-gitops` branch, run validation and security checks, and merge the Pull Request.
 
-Merge the Pull Request.
diff --git a/docs/roadmap.md b/docs/roadmap.md
index aac31fa..450bfd5 100644
--- a/docs/roadmap.md
+++ b/docs/roadmap.md
@@ -48,76 +48,71 @@ Repository now performs quality validation before every commit.
 
 ## Phase 2 — GitHub Actions Refactor
 
-Status: 🚧 In Progress
+Status: ✅ Completed
 
 Completed
 
 * Archive original workflow
-* Create ci.yml
+* Create ci.yml (validate.yml)
 * Create security.yml
 * Split validation and security responsibilities
 
-Pending
-
-* Push workflows to GitHub
-* Verify Actions
-* Fix workflow failures
-* Merge Pull Request
-
 ---
 
 ## Phase 3 — CI Improvements
 
-Planned
+Status: ✅ Completed
 
-* Composite Actions
-* Reusable Workflows
-* Dependency caching
-* Parallel jobs
-* Matrix builds
-* Artifact uploads
-* Helm caching
-* Better failure reporting
+Completed
+
+* Composite Actions (setup-helm, setup-kind, setup-kubectl, setup-kubeconform, helm-render)
+* Reusable workspace configurations
+* Modular and DRY pipelines
 
 ---
 
 ## Phase 4 — Platform Validation
 
-Planned
+Status: ✅ Completed
 
-* kubeconform
-* kube-linter
+Completed
+
+* kubeconform schema validation
 * Helm lint
-* Helm template
-* Kind integration testing
-* Kubernetes smoke tests
+* Helm template rendering
+* Kind ephemeral integration testing
+* Kubernetes smoke tests with automated HTTP status verification
 
 ---
 
 ## Phase 5 — DevSecOps
 
-Planned
+Status: ✅ Completed
 
-* Trivy
-* Trufflehog
-* Gitleaks
-* Detect Secrets
-* SBOM
-* Cosign
-* SLSA Provenance
-* OPA / Conftest
+Completed
+
+* Trivy IaC configuration scan
+* Trivy third-party image vulnerability scan
+* Gitleaks secret detection
+* Software Bill of Materials (SBOM) generation via Syft
 
 ---
 
 ## Phase 6 — GitOps
 
-Planned
+Status: 🚧 In Progress
+
+Completed
+
+* GitOps engine comparative analysis (Argo CD vs Flux CD - ADR-0004)
+* Declarative Argo CD bootstrap automation (`install-argocd.sh`)
+* Native Multiple Sources configuration to separate upstream chart and local values config (`application.yaml`)
+* Makefile integration (`argocd-bootstrap`, `argocd-status`, `argocd-port-forward`, `argocd-down`)
+
+Pending
 
-* ArgoCD
-* FluxCD comparison
 * Progressive delivery
-* Rollbacks
-* Health checks
+* Rollbacks and automated self-healing validation
 
 ---
 
@@ -226,19 +221,11 @@ By the end of this repository the following skills should be demonstrated.
 
 Current Branch
 
-feature/ci-refactor
+feature/phase4-gitops
 
 Current Objective
 
-Push the refactored GitHub Actions workflows to GitHub.
-
-Create a Pull Request.
-
-Review failures.
-
-Fix failures.
-
-Merge after validation.
+Verify declarative Argo CD bootstrapping, test multiple source Application sync, configure port-forwarding targets, and submit a Pull Request.
 
 ---
 
diff --git a/platform/argocd/application.yaml b/platform/argocd/application.yaml
new file mode 100644
index 0000000..ec52d09
--- /dev/null
+++ b/platform/argocd/application.yaml
@@ -0,0 +1,31 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: astronomy-shop
+  namespace: argocd
+  finalizers:
+    - resources-finalizer.argocd.argoproj.io
+spec:
+  project: default
+  sources:
+    # Source 1: Upstream Helm chart repository
+    - repoURL: 'https://open-telemetry.github.io/opentelemetry-helm-charts'
+      chart: opentelemetry-demo
+      targetRevision: 0.40.9
+      helm:
+        valueFiles:
+          - $values/platform/helm/values.yaml
+    # Source 2: Our Git repository containing the values overrides
+    - repoURL: 'https://github.com/letsconfuse/shop-devops.git'
+      targetRevision: HEAD
+      ref: values
+  destination:
+    server: 'https://kubernetes.default.svc'
+    namespace: astronomy-shop
+  syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true
+    syncOptions:
+      - CreateNamespace=true
+      - ApplyOutOfSyncOnly=true
diff --git a/platform/argocd/install-argocd.sh b/platform/argocd/install-argocd.sh
new file mode 100644
index 0000000..dcee841
--- /dev/null
+++ b/platform/argocd/install-argocd.sh
@@ -0,0 +1,54 @@
+#!/usr/bin/env bash
+# install-argocd.sh - Bootstrap Argo CD and deploy the application
+
+set -euo pipefail
+
+ARGOCD_VERSION="v2.11.0"
+ARGOCD_NAMESPACE="argocd"
+APP_MANIFEST="platform/argocd/application.yaml"
+
+echo "Initializing Argo CD installation (version: ${ARGOCD_VERSION})..."
+
+# Check if kubectl is available
+if ! command -v kubectl &>/dev/null; then
+  echo "Error: kubectl is not installed or not in PATH." >&2
+  exit 1
+fi
+
+# Create the namespace if it doesn't exist
+if ! kubectl get namespace "${ARGOCD_NAMESPACE}" &>/dev/null; then
+  echo "Creating namespace ${ARGOCD_NAMESPACE}..."
+  kubectl create namespace "${ARGOCD_NAMESPACE}"
+else
+  echo "Namespace ${ARGOCD_NAMESPACE} already exists."
+fi
+
+# Apply the stable Argo CD installation manifests
+echo "Applying Argo CD installation manifests..."
+kubectl apply -n "${ARGOCD_NAMESPACE}" -f "https://raw.githubusercontent.com/argoproj/argo-cd/${ARGOCD_VERSION}/manifests/install.yaml"
+
+# Wait for Argo CD components to be rolled out and ready
+echo "Waiting for Argo CD deployments to be ready..."
+deployments=(
+  "argocd-redis"
+  "argocd-repo-server"
+  "argocd-server"
+  "argocd-applicationset-controller"
+  "argocd-notifications-controller"
+)
+
+for deploy in "${deployments[@]}"; do
+  echo "Waiting for rollout of deployment/${deploy}..."
+  kubectl rollout status "deployment/${deploy}" -n "${ARGOCD_NAMESPACE}" --timeout=150s
+done
+
+echo "Argo CD has been successfully installed and is running."
+
+# Apply the Argo CD Application manifest for astronomy-shop
+if [ -f "${APP_MANIFEST}" ]; then
+  echo "Deploying the Astronomy Shop application via Argo CD..."
+  kubectl apply -f "${APP_MANIFEST}"
+  echo "Application manifest applied. Monitor status via kubectl or the Argo CD UI."
+else
+  echo "Warning: Application manifest not found at ${APP_MANIFEST}. Skipping application deployment."
+fi