diff --git a/app/ui/legacy/build.gradle.kts b/app/ui/legacy/build.gradle.kts
index 691e81b7c..293c4e3cc 100644
--- a/app/ui/legacy/build.gradle.kts
+++ b/app/ui/legacy/build.gradle.kts
@@ -5,6 +5,8 @@ plugins {
 
 dependencies {
     api(projects.app.ui.base)
+    api(projects.core.ui.legacy.designsystem)
+
     implementation(projects.app.core)
     implementation(projects.mail.common)
     implementation(projects.uiUtils.toolbarBottomSheet)
diff --git a/core/ui/legacy/README.md b/core/ui/legacy/README.md
new file mode 100644
index 000000000..369d59308
--- /dev/null
+++ b/core/ui/legacy/README.md
@@ -0,0 +1,11 @@
+## Core - UI - Legacy
+
+The modules in this section are dedicated to the legacy UI implementation based on XML-based layouts for Android.
+
+> [!WARNING]
+> It's not suggested to use the contained modules for new features!
+>
+> This is only maintained for the purpose of supporting the existing implementation.
+
+> [!IMPORTANT]
+> Use the Composable UI along our [theme 2](../compose/theme2) and [design system](../compose/designsystem) design system instead.
diff --git a/core/ui/legacy/designsystem/README.md b/core/ui/legacy/designsystem/README.md
new file mode 100644
index 000000000..e9b7a7ef7
--- /dev/null
+++ b/core/ui/legacy/designsystem/README.md
@@ -0,0 +1,11 @@
+## Core - UI - Legacy - Design System
+
+This is the design system dedicated to the legacy UI implementation based on XML-based layouts for Android.
+
+> [!WARNING]
+> It's not suggested to use this design system for new features!
+>
+> This is only maintained for the purpose of supporting the existing implementation.
+
+> [!IMPORTANT]
+> Use the Composable UI along our [theme 2](../compose/theme2) and [design system](../compose/designsystem) design system instead.
diff --git a/core/ui/legacy/designsystem/build.gradle.kts b/core/ui/legacy/designsystem/build.gradle.kts
new file mode 100644
index 000000000..5e6599511
--- /dev/null
+++ b/core/ui/legacy/designsystem/build.gradle.kts
@@ -0,0 +1,12 @@
+plugins {
+    id(ThunderbirdPlugins.Library.android)
+}
+
+android {
+    namespace = "app.k9mail.core.ui.legacy.designsystem"
+}
+
+dependencies {
+    // TODO Remove this dependency once the legacy theme is available
+    api(libs.android.material)
+}
diff --git a/settings.gradle.kts b/settings.gradle.kts
index 678e7a8cf..c4be8191a 100644
--- a/settings.gradle.kts
+++ b/settings.gradle.kts
@@ -80,6 +80,7 @@ include(
     ":core:ui:compose:theme2:k9mail",
     ":core:ui:compose:theme2:thunderbird",
     ":core:ui:compose:testing",
+    ":core:ui:legacy:designsystem",
 )
 
 include(