diff --git a/diff.go b/diff.go
new file mode 100644
index 0000000..b2a9ccd
--- /dev/null
+++ b/diff.go
@@ -0,0 +1,81 @@
+package jsonpointer
+
+import (
+	"log"
+	"reflect"
+)
+
+// DiffType represents the type of difference between two JSON
+// structures.
+type DiffType int
+
+const (
+	// MissingA designates a path that was missing from the first
+	// argument of the diff.
+	MissingA = DiffType(iota)
+	// MissingB designates a path taht was missing from the second
+	// argument of the diff.
+	MissingB
+	// Different designates a path that is found in both
+	// arguments, but with different values.
+	Different
+)
+
+var diffNames = []string{"missing a", "missing b", "different"}
+
+func (d DiffType) String() string {
+	return diffNames[d]
+}
+
+func must(err error) {
+	if err != nil {
+		log.Panic(err)
+	}
+}
+
+// Diff returns the differences between two json blobs.
+func Diff(a, b []byte) (map[string]DiffType, error) {
+	alist, err := ListPointers(a)
+	if err != nil {
+		return nil, err
+	}
+	blist, err := ListPointers(b)
+	if err != nil {
+		return nil, err
+	}
+
+	amap := map[string]bool{}
+	bmap := map[string]bool{}
+	for _, v := range alist {
+		amap[v] = true
+	}
+	for _, v := range blist {
+		bmap[v] = true
+	}
+
+	rv := map[string]DiffType{}
+
+	for _, v := range alist {
+		if v == "" {
+			continue
+		}
+		if bmap[v] {
+			var aval, bval interface{}
+			must(FindDecode(a, v, &aval))
+			must(FindDecode(b, v, &bval))
+			if !reflect.DeepEqual(aval, bval) {
+				rv[v] = Different
+			}
+		} else {
+			rv[v] = MissingB
+		}
+	}
+
+	for _, v := range blist {
+		if !amap[v] {
+			rv[v] = MissingA
+		}
+	}
+
+	return rv, nil
+}
diff --git a/diff_test.go b/diff_test.go
new file mode 100644
index 0000000..46e0b54
--- /dev/null
+++ b/diff_test.go
@@ -0,0 +1,95 @@
+package jsonpointer
+
+import (
+	"io"
+	"reflect"
+	"testing"
+)
+
+func TestDiffNil(t *testing.T) {
+	diffs, err := Diff(nil, nil)
+	if err != nil {
+		t.Fatalf("Expected no error on nil diff, got %v", err)
+	}
+	if len(diffs) != 0 {
+		t.Errorf("Expected no diffs, got %v", diffs)
+	}
+}
+
+func TestDiffNames(t *testing.T) {
+	tests := map[DiffType]string{
+		MissingA:  "missing a",
+		MissingB:  "missing b",
+		Different: "different",
+	}
+
+	for k, v := range tests {
+		if k.String() != v {
+			t.Errorf("Expected %v for %d, got %v", v, k, k)
+		}
+	}
+}
+
+func TestMust(t *testing.T) {
+	must(nil) // no panic
+	panicked := false
+	func() {
+		defer func() { panicked = recover() != nil }()
+		must(io.EOF)
+	}()
+	if !panicked {
+		t.Fatalf("Expected a panic, but didn't get one")
+	}
+}
+
+func TestDiff(t *testing.T) {
+	var (
+		aFirst = `{"a": 1, "b": 3.2}`
+		bFirst = `{"b":3.2,"a":1}`
+		aTwo   = `{"a": 2, "b": 3.2}`
+		aOnly1 = `{"a": 1}`
+		aOnly3 = `{"a": 3}`
+		broken = `{x}`
+	)
+
+	tests := []struct {
+		name    string
+		a, b    string
+		exp     map[string]DiffType
+		errored bool
+	}{
+		{"Empty", "", "", map[string]DiffType{}, false},
+		{"Identity", aFirst, aFirst, map[string]DiffType{}, false},
+		{"Same", aFirst, bFirst, map[string]DiffType{}, false},
+		{"Other order", aFirst, bFirst, map[string]DiffType{}, false},
+		{"A diff", aFirst, aTwo, map[string]DiffType{"/a": Different}, false},
+		{"A diff rev", aTwo, aFirst, map[string]DiffType{"/a": Different}, false},
+		{"Missing b <- 1", aFirst, aOnly1, map[string]DiffType{"/b": MissingB}, false},
+		{"Missing b -> 1", aOnly1, aFirst, map[string]DiffType{"/b": MissingA}, false},
+		{"Missing b <- 3", aTwo, aOnly3, map[string]DiffType{
+			"/a": Different,
+			"/b": MissingB,
+		}, false},
+		{"Missing b -> 3", aOnly3, aTwo, map[string]DiffType{
+			"/a": Different,
+			"/b": MissingA,
+		}, false},
+		{"Broken A", broken, aFirst, nil, true},
+		{"Broken B", aFirst, broken, nil, true},
+	}
+
+	for _, test := range tests {
+		diffs, err := Diff([]byte(test.a), []byte(test.b))
+		if (err != nil) != test.errored {
+			t.Errorf("Expected error=%v on %q:  %v", test.errored, test.name, err)
+		}
+		if err != nil {
+			continue
+		}
+		if !reflect.DeepEqual(test.exp, diffs) {
+			t.Errorf("Unexpected diff for %q: %v\nwanted %v",
+				test.name, diffs, test.exp)
+		}
+	}
+
+}