diff --git a/rectangle.go b/rectangle.go
index eb138e4..9c7b07b 100644
--- a/rectangle.go
+++ b/rectangle.go
@@ -54,6 +54,40 @@ func (r Rectangle) Size() float64 {
 	return distance(r.P1, n1) * distance(r.P1, n2)
 }
 
-//
-//func Containment(r1, r2, Rectangle) bool {
-//}
+func sumOfTri(r Rectangle, p Point) bool {
+	rsize := r.Size()
+	n1, n2 := r.Neighbors(r.P1)
+	x1, x2 := Point{}, Point{}
+	accross := &Point{}
+	if r.P2 != n1 || r.P2 != n2 {
+		accross = &r.P2
+		x1, x2 = r.Neighbors(r.P2)
+	}
+	if r.P3 != n1 || r.P3 != n2 {
+		accross = &r.P3
+		x1, x2 = r.Neighbors(r.P3)
+	}
+	if r.P4 != n1 || r.P4 != n2 {
+		accross = &r.P4
+		x1, x2 = r.Neighbors(r.P4)
+	}
+	sumTri := SizeTriangle(r.P1, n1, p) +
+		SizeTriangle(r.P1, n2, p) +
+		SizeTriangle(*accross, x1, p) +
+		SizeTriangle(*accross, x2, p)
+	if rsize == sumTri {
+		return true
+	}
+	return false
+}
+
+// Containment returns whether r2 is contained inside of r1
+func Containment(r1, r2 Rectangle) bool {
+	if r1.Size() <= r2.Size() {
+		return false
+	}
+	if sumOfTri(r1, r2.P1) && sumOfTri(r1, r2.P2) && sumOfTri(r1, r2.P3) && sumOfTri(r1, r2.P4) {
+		return true
+	}
+	return false
+}
diff --git a/rectangle_test.go b/rectangle_test.go
index d9fb023..a3dabe8 100644
--- a/rectangle_test.go
+++ b/rectangle_test.go
@@ -52,3 +52,46 @@ func TestSize(t *testing.T) {
 
 	}
 }
+
+func TestContainment(t *testing.T) {
+	var containmentTest = []struct {
+		r        []Rectangle
+		expected bool
+	}{
+		{
+			[]Rectangle{
+				Rectangle{Point{0, 0}, Point{0, 3}, Point{3, 0}, Point{3, 3}},
+				Rectangle{Point{1, 1}, Point{1, 2}, Point{2, 1}, Point{2, 2}}},
+			true,
+		},
+		{
+			[]Rectangle{
+				Rectangle{Point{0, 0}, Point{0, 3}, Point{3, 0}, Point{3, 3}},
+				Rectangle{Point{1, 1}, Point{1, 2}, Point{2, 1}, Point{2, 2}}},
+			true,
+		},
+		{
+			[]Rectangle{
+				Rectangle{Point{0, 0}, Point{0, 3}, Point{3, 0}, Point{3, 3}},
+				Rectangle{Point{0, 0}, Point{0, 3}, Point{3, 0}, Point{3, 3}}},
+			false,
+		},
+		{
+			[]Rectangle{
+				Rectangle{Point{0, 0}, Point{0, 3}, Point{3, 0}, Point{3, 3}},
+				Rectangle{Point{3, 3}, Point{3, 4}, Point{4, 3}, Point{4, 4}}},
+			false,
+		},
+	}
+	for _, rt := range containmentTest {
+		actual := Containment(rt.r[0], rt.r[1])
+		if actual != rt.expected {
+			t.Errorf(
+				"failed spiral:\n\texpected: %d\n\t  actual: %d",
+				rt.expected,
+				actual,
+			)
+		}
+
+	}
+}