diff --git a/lib/components_elixir/inventory.ex b/lib/components_elixir/inventory.ex
index 905add6..2083847 100644
--- a/lib/components_elixir/inventory.ex
+++ b/lib/components_elixir/inventory.ex
@@ -203,6 +203,27 @@ defmodule ComponentsElixir.Inventory do
     Category.changeset(category, attrs)
   end
 
+  @doc """
+  Gets all category IDs that are descendants of the given category ID, including the category itself.
+  This is used for filtering components by category and all its subcategories.
+  Returns an empty list if the category doesn't exist.
+
+  Note: This implementation loads all categories into memory for traversal, which is efficient
+  for typical category tree sizes (hundreds of categories). For very large category trees,
+  a recursive CTE query could be used instead.
+  """
+  def get_category_and_descendant_ids(category_id) when is_integer(category_id) do
+    categories = list_categories()
+
+    # Verify the category exists before getting descendants
+    case Enum.find(categories, &(&1.id == category_id)) do
+      nil -> []
+      _category -> ComponentsElixir.Inventory.Hierarchical.descendant_ids(categories, category_id, &(&1.parent_id))
+    end
+  end
+
+  def get_category_and_descendant_ids(_), do: []
+
   ## Components
 
   @doc """
@@ -219,7 +240,9 @@ defmodule ComponentsElixir.Inventory do
   defp apply_component_filters(query, opts) do
     Enum.reduce(opts, query, fn
       {:category_id, category_id}, query when not is_nil(category_id) ->
-        where(query, [c], c.category_id == ^category_id)
+        # Get the category and all its descendant category IDs
+        category_ids = get_category_and_descendant_ids(category_id)
+        where(query, [c], c.category_id in ^category_ids)
 
       {:storage_location_id, storage_location_id}, query when not is_nil(storage_location_id) ->
         where(query, [c], c.storage_location_id == ^storage_location_id)
diff --git a/lib/components_elixir/inventory/hierarchical.ex b/lib/components_elixir/inventory/hierarchical.ex
index d938953..02153cb 100644
--- a/lib/components_elixir/inventory/hierarchical.ex
+++ b/lib/components_elixir/inventory/hierarchical.ex
@@ -143,6 +143,32 @@ defmodule ComponentsElixir.Inventory.Hierarchical do
     end)
   end
 
+  @doc """
+  Gets all descendant IDs for a given entity ID, including the entity itself.
+  This recursively finds all children, grandchildren, etc.
+
+  ## Examples
+      iex> categories = [
+      ...>   %{id: 1, parent_id: nil},
+      ...>   %{id: 2, parent_id: 1},
+      ...>   %{id: 3, parent_id: 2},
+      ...>   %{id: 4, parent_id: 1}
+      ...> ]
+      iex> Hierarchical.descendant_ids(categories, 1, &(&1.parent_id))
+      [1, 2, 3, 4]
+  """
+  def descendant_ids(entities, entity_id, parent_id_accessor_fn) do
+    [entity_id | get_descendant_ids_recursive(entities, entity_id, parent_id_accessor_fn)]
+  end
+
+  defp get_descendant_ids_recursive(entities, parent_id, parent_id_accessor_fn) do
+    children = child_entities(entities, parent_id, parent_id_accessor_fn)
+
+    Enum.flat_map(children, fn child ->
+      [child.id | get_descendant_ids_recursive(entities, child.id, parent_id_accessor_fn)]
+    end)
+  end
+
   @doc """
   Generates display name for entity including parent context.
   For dropdown displays: "Parent > Child"