diff --git a/lib/reach/project.ex b/lib/reach/project.ex
index e733ee5..07ef902 100644
--- a/lib/reach/project.ex
+++ b/lib/reach/project.ex
@@ -31,11 +31,20 @@ defmodule Reach.Project do
           nodes: %{IR.Node.id() => IR.Node.t()},
           call_graph: Graph.t(),
           summaries: %{{module(), atom(), non_neg_integer()} => map()},
-          plugins: [module()]
+          plugins: [module()],
+          cache_key: reference() | nil
         }
 
   @enforce_keys [:modules, :graph, :nodes, :call_graph]
-  defstruct [:modules, :graph, :nodes, :call_graph, summaries: %{}, plugins: []]
+  defstruct [
+    :modules,
+    :graph,
+    :nodes,
+    :call_graph,
+    summaries: %{},
+    plugins: [],
+    cache_key: nil
+  ]
 
   @doc """
   Builds a project graph from source file paths.
@@ -312,7 +321,8 @@ defmodule Reach.Project do
       graph: Graph.new(type: :directed),
       nodes: nodes,
       call_graph: Graph.new(type: :directed),
-      plugins: plugins
+      plugins: plugins,
+      cache_key: make_ref()
     }
   end
 
@@ -403,7 +413,8 @@ defmodule Reach.Project do
       nodes: merged_nodes,
       call_graph: merged_call_graph,
       summaries: summaries,
-      plugins: plugins
+      plugins: plugins,
+      cache_key: make_ref()
     }
   end
 
diff --git a/lib/reach/project/query.ex b/lib/reach/project/query.ex
index d97884e..2d0385e 100644
--- a/lib/reach/project/query.ex
+++ b/lib/reach/project/query.ex
@@ -3,9 +3,24 @@ defmodule Reach.Project.Query do
 
   alias Reach.IR.Helpers, as: IRHelpers
 
-  def function_index(project), do: build_function_index(project)
+  @function_index_cache_key {__MODULE__, :function_index}
 
-  def reset_cache, do: :ok
+  def function_index(%{cache_key: key} = project) do
+    case Process.get(@function_index_cache_key) do
+      {^key, index} ->
+        index
+
+      _miss ->
+        index = build_function_index(project)
+        Process.put(@function_index_cache_key, {key, index})
+        index
+    end
+  end
+
+  def reset_cache do
+    Process.delete(@function_index_cache_key)
+    :ok
+  end
 
   def find_function(project, target) do
     index = function_index(project)
diff --git a/test/reach/project/query_cache_test.exs b/test/reach/project/query_cache_test.exs
index c87f77e..0e348f3 100644
--- a/test/reach/project/query_cache_test.exs
+++ b/test/reach/project/query_cache_test.exs
@@ -15,6 +15,25 @@ defmodule Reach.Project.QueryCacheTest do
     refute Query.find_function(second, {FirstOnly, :run, 0})
   end
 
+  test "function_index is memoized within a process for the same project" do
+    project = project_with("Memoized", "go")
+
+    first = Query.function_index(project)
+    second = Query.function_index(project)
+
+    assert :erts_debug.same(first, second)
+  end
+
+  test "reset_cache invalidates the cached function index" do
+    project = project_with("Resettable", "do_thing")
+
+    first = Query.function_index(project)
+    Query.reset_cache()
+    second = Query.function_index(project)
+
+    refute :erts_debug.same(first, second)
+  end
+
   defp project_with(module, function) do
     source = """
     defmodule #{module} do