diff --git a/diff/diff.go b/diff/diff.go
index 293e382..4b5d37c 100644
--- a/diff/diff.go
+++ b/diff/diff.go
@@ -18,10 +18,11 @@ package diff
 
 import (
 	"fmt"
+	"sort"
+
 	"github.com/google/go-cmp/cmp"
 	"github.com/rkosegi/yaml-toolkit/dom"
 	"github.com/rkosegi/yaml-toolkit/utils"
-	"sort"
 )
 
 type ModificationType string
@@ -153,3 +154,25 @@ func Diff(left, right dom.Container) *[]Modification {
 	sortMods(mods)
 	return &mods
 }
+
+// OverlayDocs computes semantic difference between 2 Overlay documents
+func OverlayDocs(left, right dom.OverlayDocument) map[string]*[]Modification {
+	res := make(map[string]*[]Modification)
+	lmap := left.Layers()
+	rmap := right.Layers()
+	for ln, ll := range lmap {
+		if rl, ok := rmap[ln]; ok {
+			res[ln] = Diff(ll, rl)
+		} else {
+			res[ln] = Diff(ll, dom.Builder().Container())
+		}
+	}
+	for rn, rl := range rmap {
+		if ll, ok := lmap[rn]; ok {
+			res[rn] = Diff(ll, rl)
+		} else {
+			res[rn] = Diff(dom.Builder().Container(), rl)
+		}
+	}
+	return res
+}
diff --git a/diff/diff_test.go b/diff/diff_test.go
index 3f54292..a4f4813 100644
--- a/diff/diff_test.go
+++ b/diff/diff_test.go
@@ -18,12 +18,13 @@ package diff
 
 import (
 	"bytes"
+	"strings"
+	"testing"
+
 	"github.com/google/go-cmp/cmp"
 	"github.com/rkosegi/yaml-toolkit/dom"
 	"github.com/stretchr/testify/assert"
 	"gopkg.in/yaml.v3"
-	"strings"
-	"testing"
 )
 
 func leavesEqual(l1, l2 interface{}) bool {
@@ -277,3 +278,60 @@ root:
     - item1`)
 	assert.Equal(t, 0, len(*res))
 }
+
+func TestDiffOverlayDocuments(t *testing.T) {
+	var (
+		cb dom.ContainerBuilder
+	)
+	left := dom.NewOverlayDocument()
+	cb = dom.Builder().Container()
+	cb.AddValueAt("a.b.c", dom.LeafNode(1))
+	left.Add("layer1", cb)
+	cb = dom.Builder().Container()
+	cb.AddValueAt("a.b.d", dom.LeafNode("xyz"))
+	left.Add("layer2", cb)
+	cb = dom.Builder().Container()
+	cb.AddValue("something", dom.LeafNode("A"))
+	left.Add("layer3", cb)
+
+	right := dom.NewOverlayDocument()
+	cb = dom.Builder().Container()
+	cb.AddValueAt("a.b.c", dom.LeafNode(2))
+	right.Add("layer1", cb)
+	cb = dom.Builder().Container()
+	cb.AddValue("hello", dom.LeafNode("Hi!"))
+	right.Add("layer2", cb)
+	cb = dom.Builder().Container()
+	cb.AddValue("hello", dom.LeafNode("Aloha!"))
+	right.Add("layer4", cb)
+
+	res := OverlayDocs(left, right)
+	for k, v := range res {
+		t.Logf("%s: %v", k, v)
+	}
+
+	assert.Equal(t, 4, len(res))
+	assertHasChange(t, Modification{
+		Type:     ModChange,
+		Path:     "a.b.c",
+		OldValue: 1,
+		Value:    2,
+	}, res["layer1"])
+
+	assertHasChange(t, Modification{
+		Type:  ModAdd,
+		Path:  "a.b.d",
+		Value: "xyz",
+	}, res["layer2"])
+
+	assertHasChange(t, Modification{
+		Type: ModDelete,
+		Path: "hello",
+	}, res["layer2"])
+
+	assertHasChange(t, Modification{
+		Type:  ModAdd,
+		Path:  "something",
+		Value: "A",
+	}, res["layer3"])
+}