diff --git a/sum.go b/sum.go
new file mode 100644
index 0000000..278a14f
--- /dev/null
+++ b/sum.go
@@ -0,0 +1,11 @@
+package underscore
+
+import "constraints"
+
+// Sum adds elements of the slice.
+func Sum[T constraints.Ordered](values []T) (sum T) {
+	for _, v := range values {
+		sum += v
+	}
+	return sum
+}
diff --git a/sum_test.go b/sum_test.go
new file mode 100644
index 0000000..05a2a8a
--- /dev/null
+++ b/sum_test.go
@@ -0,0 +1,15 @@
+package underscore_test
+
+import (
+	"testing"
+
+	u "github.com/rjNemo/underscore"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSum(t *testing.T) {
+	nums := []int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
+	want := 45
+
+	assert.Equal(t, want, u.Sum(nums))
+}