diff --git a/model_test.go b/model_test.go
index 54b9ed3..ed1c4b9 100644
--- a/model_test.go
+++ b/model_test.go
@@ -1,7 +1,6 @@
 package gonnx
 
 import (
-	"fmt"
 	"testing"
 
 	"github.com/advancedclimatesystems/gonnx/onnx"
@@ -97,7 +96,6 @@ func TestModel(t *testing.T) {
 	}
 
 	for _, test := range tests {
-		fmt.Println(test.path)
 		model, err := NewModelFromFile(test.path)
 		assert.Nil(t, err)
 
diff --git a/ops/cumsum/cumsum.go b/ops/cumsum/cumsum.go
new file mode 100644
index 0000000..970b928
--- /dev/null
+++ b/ops/cumsum/cumsum.go
@@ -0,0 +1,170 @@
+package cumsum
+
+import (
+	"github.com/advancedclimatesystems/gonnx/onnx"
+	"github.com/advancedclimatesystems/gonnx/ops"
+	"gorgonia.org/tensor"
+)
+
+var cumsumTypeConstraints = [][]tensor.Dtype{
+	{tensor.Int32, tensor.Int64, tensor.Uint32, tensor.Uint64, tensor.Float32, tensor.Float64},
+	{tensor.Int32, tensor.Int64},
+}
+
+// CumSum represents the ONNX cumsum operator.
+type CumSum struct {
+	ops.BaseOperator
+
+	exclusive bool
+	reverse   bool
+}
+
+// newCumSum creates a new cumsum operator.
+func newCumSum(version int, typeConstraints [][]tensor.Dtype) ops.Operator {
+	return &CumSum{
+		BaseOperator: ops.NewBaseOperator(
+			version,
+			2,
+			2,
+			typeConstraints,
+			"cumsum",
+		),
+		exclusive: false,
+		reverse:   false,
+	}
+}
+
+// Init initializes the cumsum operator.
+func (c *CumSum) Init(n *onnx.NodeProto) error {
+	for _, attr := range n.GetAttribute() {
+		switch attr.GetName() {
+		case "exclusive":
+			c.exclusive = attr.GetI() == 1
+		case "reverse":
+			c.reverse = attr.GetI() == 1
+		default:
+			return ops.ErrInvalidAttribute(attr.GetName(), c)
+		}
+	}
+
+	return nil
+}
+
+// Apply applies the cumsum operator.
+func (c *CumSum) Apply(inputs []tensor.Tensor) ([]tensor.Tensor, error) {
+	axis, err := ops.AnyToInt(inputs[1].ScalarValue())
+	if err != nil {
+		return nil, err
+	}
+
+	out, err := cumsum(inputs[0], axis, c.exclusive, c.reverse)
+	if err != nil {
+		return nil, err
+	}
+
+	return []tensor.Tensor{out}, nil
+}
+
+// Performs cumulative sum of the input elements along the given axis.
+// Exclusive means the the cumsum for position j will not include the j-th element.
+// Reverse means the cumsum will be performed in reverse order.
+func cumsum(x tensor.Tensor, axis int, exclusive, reverse bool) (tensor.Tensor, error) {
+	out, ok := x.Clone().(tensor.Tensor)
+	if !ok {
+		return nil, ops.ErrCast
+	}
+
+	nDims := len(x.Shape())
+	axis = ops.ConvertNegativeAxis(axis, nDims)
+
+	if axis < 0 || axis >= nDims {
+		return nil, ops.ErrAxisOutOfRange(0, nDims, axis)
+	}
+
+	axisSize := x.Shape()[axis]
+
+	var startValue int
+	if reverse {
+		startValue = axisSize - 1
+	} else {
+		startValue = 0
+	}
+
+	slices := make([]tensor.Slice, nDims)
+	slices[axis] = ops.NewSlicer(startValue, startValue+1)
+
+	prevView, err := x.Slice(slices...)
+	if err != nil {
+		return nil, err
+	}
+
+	prevValues := prevView.Materialize()
+
+	for i := startValue; endValueReached(i, axisSize, reverse); {
+		slices[axis] = ops.NewSlicer(i, i+1)
+
+		currentView, err := out.Slice(slices...)
+		if err != nil {
+			return nil, err
+		}
+
+		currentValues := currentView.Materialize()
+
+		switch {
+		// If exclusive is true, the first result in the cumsum opertaion is zero.
+		// We can achieve this by subtracting the current values from the current values.
+		// This way we don't have to infer the underlying type of the tensor.
+		case i == startValue && exclusive:
+			zeroValues, err := ops.Sub(currentValues, currentValues)
+			if err != nil {
+				return nil, err
+			}
+
+			err = tensor.Copy(currentView, zeroValues)
+			if err != nil {
+				return nil, err
+			}
+
+		case i != startValue && exclusive:
+			err = tensor.Copy(currentView, prevValues)
+			if err != nil {
+				return nil, err
+			}
+
+			newValues, err := ops.Add(currentValues, prevValues)
+			if err != nil {
+				return nil, err
+			}
+
+			prevValues = newValues
+		case i != startValue:
+			newValues, err := ops.Add(currentValues, prevValues)
+			if err != nil {
+				return nil, err
+			}
+
+			err = tensor.Copy(currentView, newValues)
+			if err != nil {
+				return nil, err
+			}
+
+			prevValues = newValues
+		}
+
+		if reverse {
+			i--
+		} else {
+			i++
+		}
+	}
+
+	return out, nil
+}
+
+func endValueReached(i, axisSize int, reverse bool) bool {
+	if reverse {
+		return i >= 0
+	}
+
+	return i < axisSize
+}
diff --git a/ops/cumsum/cumsum_test.go b/ops/cumsum/cumsum_test.go
new file mode 100644
index 0000000..6595b29
--- /dev/null
+++ b/ops/cumsum/cumsum_test.go
@@ -0,0 +1,118 @@
+package cumsum
+
+import (
+	"testing"
+
+	"github.com/advancedclimatesystems/gonnx/onnx"
+	"github.com/advancedclimatesystems/gonnx/ops"
+	"github.com/stretchr/testify/assert"
+	"gorgonia.org/tensor"
+)
+
+func TestCumSumInit(t *testing.T) {
+	c := &CumSum{}
+	err := c.Init(
+		&onnx.NodeProto{
+			Attribute: []*onnx.AttributeProto{
+				{Name: "exclusive", I: 1},
+				{Name: "reverse", I: 1},
+			},
+		},
+	)
+
+	assert.Nil(t, err)
+	assert.Equal(t, true, c.exclusive)
+	assert.Equal(t, true, c.reverse)
+}
+
+func TestCumSumInitDefaults(t *testing.T) {
+	c := &CumSum{}
+	err := c.Init(
+		&onnx.NodeProto{
+			Attribute: []*onnx.AttributeProto{},
+		},
+	)
+
+	assert.Nil(t, err)
+	assert.Equal(t, false, c.exclusive)
+	assert.Equal(t, false, c.reverse)
+}
+
+func TestCumSum(t *testing.T) {
+	tests := []struct {
+		version  int64
+		node     *onnx.NodeProto
+		backing  []float32
+		axis     int32
+		shape    []int
+		expected []float32
+	}{
+		{
+			11,
+			&onnx.NodeProto{
+				Attribute: []*onnx.AttributeProto{
+					{Name: "exclusive", I: 0},
+					{Name: "reverse", I: 0},
+				},
+			},
+			[]float32{1, 2, 3, 4},
+			0,
+			[]int{2, 2},
+			[]float32{1, 2, 4, 6},
+		},
+		{
+			11,
+			&onnx.NodeProto{
+				Attribute: []*onnx.AttributeProto{
+					{Name: "exclusive", I: 0},
+					{Name: "reverse", I: 0},
+				},
+			},
+			[]float32{1, 2, 3, 4},
+			1,
+			[]int{2, 2},
+			[]float32{1, 3, 3, 7},
+		},
+		{
+			11,
+			&onnx.NodeProto{
+				Attribute: []*onnx.AttributeProto{
+					{Name: "exclusive", I: 1},
+					{Name: "reverse", I: 0},
+				},
+			},
+			[]float32{1, 2, 3},
+			0,
+			[]int{3},
+			[]float32{0, 1, 3},
+		},
+		{
+			11,
+			&onnx.NodeProto{
+				Attribute: []*onnx.AttributeProto{
+					{Name: "exclusive", I: 0},
+					{Name: "reverse", I: 1},
+				},
+			},
+			[]float32{1, 2, 3},
+			0,
+			[]int{3},
+			[]float32{6, 5, 3},
+		},
+	}
+
+	for _, test := range tests {
+		inputs := []tensor.Tensor{
+			ops.TensorWithBackingFixture(test.backing, test.shape...),
+			tensor.New(tensor.FromScalar(test.axis)),
+		}
+
+		cumsum := cumsumVersions[test.version]()
+		err := cumsum.Init(test.node)
+		assert.Nil(t, err)
+
+		res, err := cumsum.Apply(inputs)
+		assert.Nil(t, err)
+		assert.Equal(t, test.expected, res[0].Data())
+	}
+}
diff --git a/ops/cumsum/versions.go b/ops/cumsum/versions.go
new file mode 100644
index 0000000..89fceab
--- /dev/null
+++ b/ops/cumsum/versions.go
@@ -0,0 +1,13 @@
+package cumsum
+
+import (
+	"github.com/advancedclimatesystems/gonnx/ops"
+)
+
+var cumsumVersions = ops.OperatorVersions{
+	11: ops.NewOperatorConstructor(newCumSum, 11, cumsumTypeConstraints),
+}
+
+func GetVersions() ops.OperatorVersions {
+	return cumsumVersions
+}
diff --git a/ops/utils.go b/ops/utils.go
index 1dcee9e..f41d911 100644
--- a/ops/utils.go
+++ b/ops/utils.go
@@ -78,6 +78,22 @@ func OffsetTensorIfNegative(t tensor.Tensor, offset int) error {
 	return nil
 }
 
+// AnyToInt casts the given data to an int, but only if the data is of some sort of int type.
+func AnyToInt(value interface{}) (int, error) {
+	switch data := value.(type) {
+	case int8:
+		return int(data), nil
+	case int16:
+		return int(data), nil
+	case int32:
+		return int(data), nil
+	case int64:
+		return int(data), nil
+	default:
+		return 0, ErrCast
+	}
+}
+
 // AnyToIntSlice casts the data of a node to an int list. This will only
 // be done if the data is of some sort of int type.
 func AnyToIntSlice(value interface{}) ([]int, error) {
diff --git a/ops_test.go b/ops_test.go
index 07fb258..1a7df89 100644
--- a/ops_test.go
+++ b/ops_test.go
@@ -402,6 +402,13 @@ var expectedTests = []string{
 	"test_cos_example",
 	"test_cosh",
 	"test_cosh_example",
+	"test_cumsum_1d",
+	"test_cumsum_1d_exclusive",
+	"test_cumsum_1d_reverse",
+	"test_cumsum_1d_reverse_exclusive",
+	"test_cumsum_2d_axis_0",
+	"test_cumsum_2d_axis_1",
+	"test_cumsum_2d_negative_axis",
 	"test_div",
 	"test_div_bcast",
 	"test_div_example",
diff --git a/opset.go b/opset.go
index 0bfcdb9..4542915 100644
--- a/opset.go
+++ b/opset.go
@@ -19,6 +19,7 @@ import (
 	"github.com/advancedclimatesystems/gonnx/ops/conv"
 	"github.com/advancedclimatesystems/gonnx/ops/cos"
 	"github.com/advancedclimatesystems/gonnx/ops/cosh"
+	"github.com/advancedclimatesystems/gonnx/ops/cumsum"
 	"github.com/advancedclimatesystems/gonnx/ops/div"
 	"github.com/advancedclimatesystems/gonnx/ops/equal"
 	"github.com/advancedclimatesystems/gonnx/ops/expand"
@@ -85,6 +86,7 @@ var operators = map[string]ops.OperatorVersions{
 	"Conv":            conv.GetConvVersions(),
 	"Cos":             cos.GetCosVersions(),
 	"Cosh":            cosh.GetCoshVersions(),
+	"CumSum":          cumsum.GetVersions(),
 	"Div":             div.GetDivVersions(),
 	"Equal":           equal.GetEqualVersions(),
 	"Expand":          expand.GetExpandVersions(),