diff --git a/Changes.md b/Changes.md
index f1cbee4..adc587d 100644
--- a/Changes.md
+++ b/Changes.md
@@ -1,5 +1,6 @@
 ## 0.0.6  2021-03-27
 
+* Added a `d.IsNot` assertion.
 * Clarified that `d.ValueIs` only accepts literal values as its second
   argument, not a `Comparer`.
 
diff --git a/pkg/detest/basic.go b/pkg/detest/basic.go
index ce8cc4f..7538632 100644
--- a/pkg/detest/basic.go
+++ b/pkg/detest/basic.go
@@ -9,7 +9,8 @@ import (
 	"strconv"
 )
 
-// ExactEqualityComparer implements exact comparison of two values.
+// ExactEqualityComparer implements exact comparison of two values, checking
+// that they're equal.
 type ExactEqualityComparer struct {
 	expect interface{}
 }
@@ -52,6 +53,22 @@ func (d *D) Passes(actual interface{}, expect Comparer, args ...interface{}) boo
 	return d.ok(argsToName(args, "unnamed d.Passes call"))
 }
 
+// IsNot tests that two variables are not exactly equal. The first variable is
+// the actual variable and the second is what is expected. The `expect` must
+// be a literal value.
+//
+// The final arguments follow the same rules as `d.Is`.
+//
+// Under the hood this is implemented with the ExactInequalityComparer.
+func (d *D) IsNot(actual, expect interface{}, args ...interface{}) bool {
+	d.ResetState()
+	d.PushActual(actual)
+	defer d.PopActual()
+
+	d.NotEqual(expect).Compare(d)
+	return d.ok(argsToName(args, "unnamed d.IsNot call"))
+}
+
 // Require takes a boolean and calls t.Fatal if it's false. The typical use is
 // to write something like:
 //
@@ -112,6 +129,49 @@ func (eec ExactEqualityComparer) Compare(d *D) {
 	d.AddResult(result)
 }
 
+// ExactInequalityComparer implements exact comparison of two values, checking
+// that they're not equal.
+type ExactInequalityComparer struct {
+	expect interface{}
+}
+
+// NotEqual takes an expected literal value and returns an
+// ExactInequalityComparer for later use.
+func (d *D) NotEqual(expect interface{}) ExactInequalityComparer {
+	return ExactInequalityComparer{expect}
+}
+
+// Compare compares the value in d.Actual() to the expected value passed to
+// Equal().
+func (eic ExactInequalityComparer) Compare(d *D) {
+	actual := d.Actual()
+	actualType := reflect.TypeOf(actual)
+	d.PushPath(d.NewPath(describeType(actualType), 1, "detest.(*D).NotEqual"))
+	defer d.PopPath()
+
+	expect := eic.expect
+	result := result{
+		actual: newValue(actual),
+		expect: newValue(expect),
+		op:     "==",
+	}
+
+	expectType := reflect.TypeOf(expect)
+	if actualType == expectType {
+		result.pass = !exactCompare(actual, expect)
+		if !result.pass {
+			result.where = inValue
+		}
+	} else {
+		result.pass = !nilValuesAreEqual(actual, expect)
+		if result.pass {
+			result.where = inType
+		}
+	}
+
+	d.AddResult(result)
+}
+
 func nilValuesAreEqual(actual, expect interface{}) bool {
 	actualValue := reflect.ValueOf(actual)
 	expectValue := reflect.ValueOf(expect)
diff --git a/pkg/detest/basic_test.go b/pkg/detest/basic_test.go
index 48dba41..a698606 100644
--- a/pkg/detest/basic_test.go
+++ b/pkg/detest/basic_test.go
@@ -28,7 +28,7 @@ func TestIs(t *testing.T) {
 		mT.AssertCalled(t, "Fail")
 	})
 
-	t.Run("Equivalent values do not compare as true", func(t *testing.T) {
+	t.Run("Equivalent values do not compare as equal", func(t *testing.T) {
 		mT := new(mockT)
 		d := NewWithOutput(mT, mT)
 		d.Is(int32(1), int64(2), "int32(1) == int64(2)")
@@ -59,6 +59,38 @@ func TestIs(t *testing.T) {
 	})
 }
 
+func TestIsNot(t *testing.T) {
+	t.Run("Passing test", func(t *testing.T) {
+		mT := new(mockT)
+		d := NewWithOutput(mT, mT)
+		d.IsNot(1, 42, "1 != 42")
+		mT.AssertNotCalled(t, "Fail")
+		mT.AssertCalled(t, "WriteString", "Assertion ok: 1 != 42\n")
+	})
+
+	t.Run("Failing test", func(t *testing.T) {
+		mT := new(mockT)
+		d := NewWithOutput(mT, mT)
+		d.IsNot(1, 1, "1 != 1")
+		mT.AssertCalled(t, "Fail")
+	})
+
+	t.Run("Equivalent values do not compare as equal", func(t *testing.T) {
+		mT := new(mockT)
+		d := NewWithOutput(mT, mT)
+		d.IsNot(int32(1), int64(2), "int32(1) != int64(2)")
+		mT.AssertNotCalled(t, "Fail")
+		mT.AssertCalled(t, "WriteString", "Assertion ok: int32(1) != int64(2)\n")
+	})
+
+	t.Run("Can handle nil", func(t *testing.T) {
+		mT := new(mockT)
+		d := NewWithOutput(mT, mT)
+		d.IsNot(nil, nil, "nil != nil")
+		mT.AssertCalled(t, "Fail")
+	})
+}
+
 // Go has this (so great) thing where there are different types of nils. A
 // bare `nil` is not the same as a nil which comes from a types but
 // uninitialized variable. But they should compare the same. Previously detest
@@ -95,6 +127,20 @@ func TestIsNilTypeHandling(t *testing.T) {
 			mT.AssertCalled(t, "WriteString", "Assertion ok: nil == uninit\n")
 		})
 
+		t.Run(fmt.Sprintf("IsNot(%s == nil)", desc), func(t *testing.T) {
+			mT := new(mockT)
+			d := NewWithOutput(mT, mT)
+
+			d.IsNot(v, nil, "uninit != nil")
+			mT.AssertCalled(t, "Fail")
+		})
+		t.Run(fmt.Sprintf("IsNot(nil == %s)", desc), func(t *testing.T) {
+			mT := new(mockT)
+			d := NewWithOutput(mT, mT)
+			d.IsNot(nil, v, "nil != uninit")
+			mT.AssertCalled(t, "Fail")
+		})
+
 		t.Run(fmt.Sprintf("ValueIs(%s == nil)", desc), func(t *testing.T) {
 			mT := new(mockT)
 			d := NewWithOutput(mT, mT)
@@ -120,13 +166,19 @@ func TestIsNilTypeHandling(t *testing.T) {
 		for _, v2 := range []interface{}{sl, ma, f, p, up, c} {
 			desc2 := describe(v2)
 			if desc != desc2 {
-				t.Run(fmt.Sprintf("Is(%s != %s)", desc, desc2), func(t *testing.T) {
+				t.Run(fmt.Sprintf("Is(%s == %s)", desc, desc2), func(t *testing.T) {
 					mT := new(mockT)
 					d := NewWithOutput(mT, mT)
 					d.Is(v, v2, "nil == uninit")
 					mT.AssertCalled(t, "Fail")
 				})
-				t.Run(fmt.Sprintf("ValueIs(%s != %s)", desc, desc2), func(t *testing.T) {
+				t.Run(fmt.Sprintf("IsNot(%s == %s)", desc, desc2), func(t *testing.T) {
+					mT := new(mockT)
+					d := NewWithOutput(mT, mT)
+					d.IsNot(v, v2, "nil != uninit")
+					mT.AssertNotCalled(t, "Fail")
+				})
+				t.Run(fmt.Sprintf("ValueIs(%s == %s)", desc, desc2), func(t *testing.T) {
 					mT := new(mockT)
 					d := NewWithOutput(mT, mT)
 					d.ValueIs(v, v2, "nil == uninit")