diff --git a/cmd/cancel.go b/cmd/cancel.go
new file mode 100644
index 000000000..2dd922f11
--- /dev/null
+++ b/cmd/cancel.go
@@ -0,0 +1,72 @@
+// Copyright 2016-2018, Pulumi Corporation.  All rights reserved.
+
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/pkg/errors"
+	"github.com/spf13/cobra"
+
+	"github.com/pulumi/pulumi/pkg/backend/cloud"
+	"github.com/pulumi/pulumi/pkg/diag/colors"
+	"github.com/pulumi/pulumi/pkg/tokens"
+	"github.com/pulumi/pulumi/pkg/util/cmdutil"
+)
+
+func newCancelCmd() *cobra.Command {
+	var yes bool
+	var cmd = &cobra.Command{
+		Use:   "cancel [<stack-name>]",
+		Args:  cmdutil.MaximumNArgs(1),
+		Short: "Cancel a stack's currently running update, if any",
+		Long: "Cancel a stack's currently running, if any.\n" +
+			"\n" +
+			"This command cancels the update currently being applied to a stack if any exists.\n" +
+			"Note that this operation is _very dangerous_, and may leave the stack in an\n" +
+			"inconsistent state if a resource operation was pending when the update was canceled.\n" +
+			"\n" +
+			"After this command completes successfully, the stack will be ready for further\n" +
+			"updates.",
+		Run: cmdutil.RunFunc(func(cmd *cobra.Command, args []string) error {
+			// Use the stack provided or, if missing, default to the current one.
+			var stack tokens.QName
+			if len(args) > 0 {
+				stack = tokens.QName(args[0])
+			}
+			s, err := requireStack(stack, false)
+			if err != nil {
+				return err
+			}
+
+			// Ensure that we are targeting the Pulumi cloud.
+			backend, ok := s.Backend().(cloud.Backend)
+			if !ok {
+				return errors.New("the `cancel` command is not supported for local stacks")
+			}
+
+			// Ensure the user really wants to do this.
+			prompt := fmt.Sprintf("This will irreversably cancel the currently running update for '%s'!", s.Name())
+			if !yes && !confirmPrompt(prompt, string(s.Name())) {
+				return errors.New("confirmation declined")
+			}
+
+			// Cancel the update.
+			if err := backend.CancelCurrentUpdate(s.Name()); err != nil {
+				return err
+			}
+
+			msg := fmt.Sprintf("%sThe currently running update for '%s' has been canceled!%s", colors.SpecAttention, s.Name(),
+				colors.Reset)
+			fmt.Println(colors.ColorizeText(msg))
+
+			return nil
+		}),
+	}
+
+	cmd.PersistentFlags().BoolVar(
+		&yes, "yes", false,
+		"Skip confirmation prompts, and proceed with cancellation anyway")
+
+	return cmd
+}
diff --git a/cmd/pulumi.go b/cmd/pulumi.go
index 7909edfd9..86660daf7 100644
--- a/cmd/pulumi.go
+++ b/cmd/pulumi.go
@@ -78,6 +78,7 @@ func NewPulumiCmd() *cobra.Command {
 	cmd.PersistentFlags().IntVarP(
 		&verbose, "verbose", "v", 0, "Enable verbose logging (e.g., v=3); anything >3 is very verbose")
 
+	cmd.AddCommand(newCancelCmd())
 	cmd.AddCommand(newConfigCmd())
 	cmd.AddCommand(newDestroyCmd())
 	cmd.AddCommand(newHistoryCmd())
diff --git a/pkg/backend/cloud/backend.go b/pkg/backend/cloud/backend.go
index b4f0f6f0e..7808c6192 100644
--- a/pkg/backend/cloud/backend.go
+++ b/pkg/backend/cloud/backend.go
@@ -119,6 +119,8 @@ type Backend interface {
 	DownloadPlugin(info workspace.PluginInfo, progress bool) (io.ReadCloser, error)
 	DownloadTemplate(name string, progress bool) (io.ReadCloser, error)
 	ListTemplates() ([]workspace.Template, error)
+
+	CancelCurrentUpdate(stackName tokens.QName) error
 }
 
 type cloudBackend struct {
@@ -788,6 +790,27 @@ func (b *cloudBackend) runEngineAction(
 	return err
 }
 
+func (b *cloudBackend) CancelCurrentUpdate(stackName tokens.QName) error {
+	stackID, err := getCloudStackIdentifier(stackName)
+	if err != nil {
+		return err
+	}
+	stack, err := b.client.GetStack(stackID)
+	if err != nil {
+		return err
+	}
+
+	// Compute the update identifier and attempt to cancel the update.
+	//
+	// NOTE: the update kind is not relevant; the same endpoint will work for updates of all kinds.
+	updateID := client.UpdateIdentifier{
+		StackIdentifier: stackID,
+		UpdateKind:      client.UpdateKindUpdate,
+		UpdateID:        stack.ActiveUpdate,
+	}
+	return b.client.CancelUpdate(updateID)
+}
+
 func (b *cloudBackend) GetHistory(stackName tokens.QName) ([]backend.UpdateInfo, error) {
 	stack, err := getCloudStackIdentifier(stackName)
 	if err != nil {
diff --git a/pkg/backend/cloud/client/client.go b/pkg/backend/cloud/client/client.go
index 4ed71b42f..724bdf261 100644
--- a/pkg/backend/cloud/client/client.go
+++ b/pkg/backend/cloud/client/client.go
@@ -430,6 +430,11 @@ func (pc *Client) PatchUpdateCheckpoint(update UpdateIdentifier, deployment *api
 	return pc.updateRESTCall("PATCH", getUpdatePath(update, "checkpoint"), nil, req, nil, updateAccessToken(token))
 }
 
+// CancelUpdate cancels the indicated update.
+func (pc *Client) CancelUpdate(update UpdateIdentifier) error {
+	return pc.restCall("POST", getUpdatePath(update, "cancel"), nil, nil, nil)
+}
+
 // CompleteUpdate completes the indicated update with the given status.
 func (pc *Client) CompleteUpdate(update UpdateIdentifier, status apitype.UpdateStatus, token string) error {
 	req := apitype.CompleteUpdateRequest{