diff --git a/OpenNest.Engine/LeadInAssigner.cs b/OpenNest.Engine/LeadInAssigner.cs
new file mode 100644
index 0000000..ae09aa5
--- /dev/null
+++ b/OpenNest.Engine/LeadInAssigner.cs
@@ -0,0 +1,40 @@
+using OpenNest.Engine.Sequencing;
+using OpenNest.Geometry;
+using System.Linq;
+
+namespace OpenNest.Engine
+{
+    public class LeadInAssigner
+    {
+        public IPartSequencer Sequencer { get; set; }
+
+        public void Assign(Plate plate)
+        {
+            var parameters = plate.CuttingParameters;
+            if (parameters == null)
+                return;
+
+            var sequenced = Sequencer.Sequence(plate.Parts.ToList(), plate);
+            var currentPoint = PlateHelper.GetExitPoint(plate);
+
+            foreach (var sp in sequenced)
+            {
+                var part = sp.Part;
+
+                if (part.LeadInsLocked)
+                {
+                    currentPoint = part.Location;
+                    continue;
+                }
+
+                if (part.HasManualLeadIns)
+                    part.RemoveLeadIns();
+
+                var localApproach = currentPoint - part.Location;
+                part.ApplyLeadIns(parameters, localApproach);
+
+                currentPoint = part.Location;
+            }
+        }
+    }
+}
diff --git a/OpenNest.Tests/LeadInAssignerTests.cs b/OpenNest.Tests/LeadInAssignerTests.cs
new file mode 100644
index 0000000..877206d
--- /dev/null
+++ b/OpenNest.Tests/LeadInAssignerTests.cs
@@ -0,0 +1,98 @@
+using OpenNest.CNC;
+using OpenNest.CNC.CuttingStrategy;
+using OpenNest.Engine;
+using OpenNest.Engine.Sequencing;
+using OpenNest.Geometry;
+
+namespace OpenNest.Tests;
+
+public class LeadInAssignerTests
+{
+    private static Part MakeSquarePartAt(double x, double y)
+    {
+        var pgm = new Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 10)));
+        pgm.Codes.Add(new LinearMove(new Vector(10, 10)));
+        pgm.Codes.Add(new LinearMove(new Vector(10, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 0)));
+        var drawing = new Drawing("test", pgm);
+        return new Part(drawing, new Vector(x, y));
+    }
+
+    [Fact]
+    public void Assign_SetsHasManualLeadInsOnAllParts()
+    {
+        var plate = new Plate(60, 120);
+        plate.Parts.Add(MakeSquarePartAt(10, 10));
+        plate.Parts.Add(MakeSquarePartAt(30, 30));
+        plate.CuttingParameters = new CuttingParameters
+        {
+            ExternalLeadIn = new LineLeadIn { Length = 0.5, ApproachAngle = 90 }
+        };
+
+        var assigner = new LeadInAssigner { Sequencer = new LeftSideSequencer() };
+        assigner.Assign(plate);
+
+        Assert.All(plate.Parts, p => Assert.True(p.HasManualLeadIns));
+    }
+
+    [Fact]
+    public void Assign_SkipsLockedParts()
+    {
+        var plate = new Plate(60, 120);
+        var lockedPart = MakeSquarePartAt(10, 10);
+        lockedPart.LeadInsLocked = true;
+        lockedPart.HasManualLeadIns = true;
+        var originalProgram = lockedPart.Program;
+
+        plate.Parts.Add(lockedPart);
+        plate.Parts.Add(MakeSquarePartAt(30, 30));
+        plate.CuttingParameters = new CuttingParameters
+        {
+            ExternalLeadIn = new LineLeadIn { Length = 0.5, ApproachAngle = 90 }
+        };
+
+        var assigner = new LeadInAssigner { Sequencer = new LeftSideSequencer() };
+        assigner.Assign(plate);
+
+        Assert.Same(originalProgram, lockedPart.Program);
+    }
+
+    [Fact]
+    public void Assign_RemovesExistingLeadInsBeforeReapply()
+    {
+        var plate = new Plate(60, 120);
+        plate.Parts.Add(MakeSquarePartAt(10, 10));
+        plate.CuttingParameters = new CuttingParameters
+        {
+            ExternalLeadIn = new LineLeadIn { Length = 0.5, ApproachAngle = 90 }
+        };
+
+        var assigner = new LeadInAssigner { Sequencer = new LeftSideSequencer() };
+        assigner.Assign(plate);
+        var countAfterFirst = plate.Parts[0].Program.Codes.Count;
+
+        assigner.Assign(plate);
+        var countAfterSecond = plate.Parts[0].Program.Codes.Count;
+
+        Assert.Equal(countAfterFirst, countAfterSecond);
+    }
+
+    [Fact]
+    public void Assign_PartsContainLeadinLayerCodes()
+    {
+        var plate = new Plate(60, 120);
+        plate.Parts.Add(MakeSquarePartAt(10, 10));
+        plate.CuttingParameters = new CuttingParameters
+        {
+            ExternalLeadIn = new LineLeadIn { Length = 0.5, ApproachAngle = 90 }
+        };
+
+        var assigner = new LeadInAssigner { Sequencer = new LeftSideSequencer() };
+        assigner.Assign(plate);
+
+        var hasLeadin = plate.Parts[0].Program.Codes.OfType<LinearMove>().Any(m => m.Layer == LayerType.Leadin);
+        Assert.True(hasLeadin);
+    }
+}