diff --git a/Source/DotNET/Model/Profiles/UiProfile.cs b/Source/DotNET/Model/Profiles/UiProfile.cs
index 68da08c..fb7e6b2 100644
--- a/Source/DotNET/Model/Profiles/UiProfile.cs
+++ b/Source/DotNET/Model/Profiles/UiProfile.cs
@@ -6,13 +6,36 @@
 namespace Cratis.Scene.Model.Profiles;
 
 /// <summary>
-/// A named target: a platform, a default size class, and an ordered list of component packages. Declaration
-/// order in <see cref="Packages"/> is override priority — a later package shadows an earlier one when both
-/// resolve the same bare component name. <c>core</c> is always the final fallback, so a minimum vocabulary
-/// resolves regardless of which packages a profile lists.
+/// A named target: a platform, a default size class, an ordered list of component packages, and the
+/// application shell and visual theme it selects. Declaration order in <see cref="Packages"/> is override
+/// priority - a later package shadows an earlier one when both resolve the same bare component name.
+/// <c>core</c> is always the final fallback, so a minimum vocabulary resolves regardless of which packages
+/// a profile lists.
 /// </summary>
 /// <param name="Name">The profile's name.</param>
 /// <param name="TargetPlatform">The platform this profile targets (e.g. <c>web</c>, <c>ios</c>, <c>android</c>, <c>desktop</c>).</param>
 /// <param name="Packages">The component packages this profile draws from, in override-priority order.</param>
 /// <param name="DefaultSizeClass">The size class assumed when the renderer cannot otherwise determine one.</param>
-public record UiProfile(string Name, string TargetPlatform, IReadOnlyList<string> Packages, SizeClass? DefaultSizeClass = null);
+/// <param name="Layout">
+/// The name of the <see cref="Layouts.Layout"/> this profile renders inside - the application's base
+/// navigational shell, normally provided by a <see cref="Packages.PackageKind.Blueprint"/> in
+/// <paramref name="Packages"/>. <see langword="null"/> when the profile does not select one.
+/// </param>
+/// <param name="Theme">
+/// The name of the <see cref="Theme"/> this profile applies, or <see langword="null"/> when it selects
+/// none. A theme is only meaningful relative to a set of packages, which is why it is chosen here rather
+/// than by a screen.
+/// </param>
+/// <remarks>
+/// A profile is where the choices that make a description concrete are made: which component vocabulary,
+/// which shell, which theme. Deliberately none of them are stated by a <see cref="Screens.Screen"/> - that
+/// is what keeps a screen portable across targets, and what lets one application ship a different shell to
+/// the web than to a phone.
+/// </remarks>
+public record UiProfile(
+    string Name,
+    string TargetPlatform,
+    IReadOnlyList<string> Packages,
+    SizeClass? DefaultSizeClass = null,
+    string? Layout = null,
+    string? Theme = null);
diff --git a/Source/JavaScript/model/profiles/UiProfile.ts b/Source/JavaScript/model/profiles/UiProfile.ts
index 0de53ba..4904acc 100644
--- a/Source/JavaScript/model/profiles/UiProfile.ts
+++ b/Source/JavaScript/model/profiles/UiProfile.ts
@@ -4,16 +4,55 @@
 import { SizeClass } from '../sizeClasses';
 
 /**
- * A named target: a platform, a default size class, and an ordered list of component packages.
- * Declaration order in `packages` is override priority — a later package shadows an earlier one when
- * both resolve the same bare component name. `core` is always the final fallback, so a minimum
- * vocabulary resolves regardless of which packages a profile lists.
+ * A named target: a platform, a default size class, an ordered list of component packages, and the
+ * application shell and visual theme it selects. Declaration order in `packages` is override priority — a
+ * later package shadows an earlier one when both resolve the same bare component name. `core` is always
+ * the final fallback, so a minimum vocabulary resolves regardless of which packages a profile lists.
+ *
+ * A profile is where the choices that make a description concrete are made: which component vocabulary,
+ * which shell, which theme. Deliberately none of them are stated by a {@link Screen} — that is what keeps
+ * a screen portable across targets, and what lets one application ship a different shell to the web than
+ * to a phone.
  */
 export interface UiProfile {
+    /**
+     * The profile's name.
+     */
     name: string;
+
+    /**
+     * The platform this profile targets (e.g. `web`, `ios`, `android`, `desktop`).
+     */
     targetPlatform: string;
+
+    /**
+     * The component packages this profile draws from, in override-priority order.
+     */
     packages: string[];
+
+    /**
+     * The size class assumed when the renderer cannot otherwise determine one.
+     */
     defaultSizeClass?: SizeClass;
+
+    /**
+     * The name of the {@link Layout} this profile renders inside — the application's base navigational
+     * shell, normally provided by a blueprint in `packages`. Absent when the profile does not select one.
+     */
+    layout?: string;
+
+    /**
+     * The name of the {@link Theme} this profile applies, or absent when it selects none. A theme is only
+     * meaningful relative to a set of packages, which is why it is chosen here rather than by a screen.
+     */
+    theme?: string;
 }
 
-export const UiProfilePropertyNames: (keyof UiProfile)[] = ['name', 'targetPlatform', 'packages', 'defaultSizeClass'];
+export const UiProfilePropertyNames: (keyof UiProfile)[] = [
+    'name',
+    'targetPlatform',
+    'packages',
+    'defaultSizeClass',
+    'layout',
+    'theme',
+];
diff --git a/scene-model-shape.json b/scene-model-shape.json
index 7b9dab9..1e1a988 100644
--- a/scene-model-shape.json
+++ b/scene-model-shape.json
@@ -179,7 +179,9 @@
             "name",
             "targetPlatform",
             "packages",
-            "defaultSizeClass"
+            "defaultSizeClass",
+            "layout",
+            "theme"
         ],
         "Theme": [
             "name",