diff --git a/IMPLEMENTATION.md b/IMPLEMENTATION.md
index 66ede0e..bdd36be 100644
--- a/IMPLEMENTATION.md
+++ b/IMPLEMENTATION.md
@@ -51,7 +51,7 @@ Each type lives in `src/FrameProcessor/Domain/`. Tests in `tests/FrameProcessor.
 - `enum { Landscape, Portrait }`.
 - JSON converter reading/writing kebab-case lowercase.
 
-### [ ] 1.4 `Resolution`
+### [x] 1.4 `Resolution`
 - `record(int Width, int Height)`.
 - `Resolution ForOrientation(Orientation o)` — swaps when portrait.
 
diff --git a/src/FrameProcessor/Domain/Resolution.cs b/src/FrameProcessor/Domain/Resolution.cs
new file mode 100644
index 0000000..66363ff
--- /dev/null
+++ b/src/FrameProcessor/Domain/Resolution.cs
@@ -0,0 +1,11 @@
+namespace FrameProcessor.Domain;
+
+public sealed record Resolution(int Width, int Height)
+{
+    public Resolution ForOrientation(Orientation orientation) => orientation switch
+    {
+        Orientation.Landscape => this,
+        Orientation.Portrait => new Resolution(Height, Width),
+        _ => throw new ArgumentOutOfRangeException(nameof(orientation), orientation, null),
+    };
+}
diff --git a/tests/FrameProcessor.Tests/ResolutionTests.cs b/tests/FrameProcessor.Tests/ResolutionTests.cs
new file mode 100644
index 0000000..89bd98b
--- /dev/null
+++ b/tests/FrameProcessor.Tests/ResolutionTests.cs
@@ -0,0 +1,44 @@
+using FrameProcessor.Domain;
+
+namespace FrameProcessor.Tests;
+
+public class ResolutionTests
+{
+    [Fact]
+    public void Constructor_StoresWidthAndHeight()
+    {
+        var resolution = new Resolution(1600, 1200);
+
+        Assert.Equal(1600, resolution.Width);
+        Assert.Equal(1200, resolution.Height);
+    }
+
+    [Fact]
+    public void ForOrientation_Landscape_ReturnsSameDimensions()
+    {
+        var resolution = new Resolution(1600, 1200);
+
+        var oriented = resolution.ForOrientation(Orientation.Landscape);
+
+        Assert.Equal(1600, oriented.Width);
+        Assert.Equal(1200, oriented.Height);
+    }
+
+    [Fact]
+    public void ForOrientation_Portrait_SwapsWidthAndHeight()
+    {
+        var resolution = new Resolution(1600, 1200);
+
+        var oriented = resolution.ForOrientation(Orientation.Portrait);
+
+        Assert.Equal(1200, oriented.Width);
+        Assert.Equal(1600, oriented.Height);
+    }
+
+    [Fact]
+    public void Equality_BasedOnWidthAndHeight()
+    {
+        Assert.Equal(new Resolution(1600, 1200), new Resolution(1600, 1200));
+        Assert.NotEqual(new Resolution(1600, 1200), new Resolution(1200, 1600));
+    }
+}