diff --git a/actions/sync.go b/actions/sync.go
new file mode 100644
index 0000000..0299702
--- /dev/null
+++ b/actions/sync.go
@@ -0,0 +1,172 @@
+package actions
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	"github.com/bitcomplete/plz-cli/client/deps"
+	"github.com/go-git/go-git/v5"
+	"github.com/go-git/go-git/v5/config"
+	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/pkg/errors"
+	"github.com/shurcooL/graphql"
+	"github.com/urfave/cli/v2"
+)
+
+type syncReview struct {
+	ID           string `graphql:"id"`
+	Status       string `graphql:"status"`
+	HeadBranch   string `graphql:"headBranch"`
+	RevisionList struct {
+		Revisions []struct {
+			Parent *struct {
+				Number int `graphql:"number"`
+				Review struct {
+					ID string `graphql:"id"`
+				} `graphql:"review"`
+			} `graphql:"parent"`
+		} `graphql:"revisions"`
+	} `graphql:"revisionList(options: {count: 1})"`
+}
+
+type syncUpdatedReview struct {
+	HeadBranch   string `graphql:"headBranch"`
+	RevisionList struct {
+		Revisions []struct {
+			Number        int    `graphql:"number"`
+			HeadCommitSHA string `graphql:"headCommitSha"`
+			BaseBranch    string `graphql:"baseBranch"`
+			BaseCommitSHA string `graphql:"baseCommitSha"`
+		} `graphql:"revisions"`
+	} `graphql:"revisionList(options: {count: 1})"`
+}
+
+func loadSyncReview(ctx context.Context, graphqlClient *graphql.Client, reviewID string) (*syncReview, error) {
+	var query struct {
+		Review syncReview `graphql:"review(id: $reviewID)"`
+	}
+	err := graphqlClient.Query(ctx, &query, map[string]interface{}{
+		"reviewID": graphql.ID(reviewID),
+	})
+	if err != nil {
+		return nil, errors.WithStack(err)
+	}
+	return &query.Review, nil
+}
+
+func Sync(c *cli.Context) error {
+	ctx := c.Context
+	deps := deps.FromContext(ctx)
+
+	token, err := deps.Auth.Token()
+	if err != nil {
+		return err
+	}
+	gitHubRepo, err := newGitHubRepo(ctx, token)
+	if err != nil {
+		return err
+	}
+	graphqlClient := graphql.NewClient(deps.PlzAPIBaseURL+"/api/v1", &http.Client{
+		Transport: &authTransport{Token: token},
+	})
+
+	if err := checkCleanWorktree(ctx, gitHubRepo); err != nil {
+		return err
+	}
+
+	headRef, err := gitHubRepo.GitRepo().Head()
+	if err != nil {
+		return errors.WithStack(err)
+	}
+	deps.DebugLog.Println("HEAD is at", headRef.Hash())
+	repo := gitHubRepo.GitRepo()
+	headCommit, err := repo.CommitObject(headRef.Hash())
+	if err != nil {
+		return errors.WithStack(err)
+	}
+	reviewID := readReviewIDFromCommitMessage(headCommit.Message)
+	if reviewID == "" {
+		return errors.New("HEAD commit has no review")
+	}
+	var reviews []*syncReview
+	for reviewID != "" {
+		deps.DebugLog.Println("loading review", reviewID)
+		review, err := loadSyncReview(ctx, graphqlClient, reviewID)
+		if err != nil {
+			return err
+		}
+		if review.Status != "open" {
+			break
+		}
+		reviews = append(reviews, review)
+		parent := review.RevisionList.Revisions[0].Parent
+		if parent == nil {
+			break
+		}
+		reviewID = parent.Review.ID
+	}
+
+	remote, err := repo.Remote(git.DefaultRemoteName)
+	if err != nil {
+		return errors.WithStack(err)
+	}
+	updatedReviews := make([]*syncUpdatedReview, len(reviews))
+	for i := len(reviews) - 1; i >= 0; i-- {
+		review := reviews[i]
+		var mutation struct {
+			Review syncUpdatedReview `graphql:"syncReviewWithParent(reviewID: $reviewID)"`
+		}
+		deps.DebugLog.Println("syncing review", review.ID)
+		err = graphqlClient.Mutate(ctx, &mutation, map[string]interface{}{
+			"reviewID": graphql.ID(review.ID),
+		})
+		if err != nil {
+			return errors.WithStack(err)
+		}
+		updatedReviews[i] = &mutation.Review
+
+		refName := plumbing.NewRemoteReferenceName(git.DefaultRemoteName, review.HeadBranch)
+		ref, err := repo.Reference(refName, true)
+		if err != nil {
+			return errors.WithStack(err)
+		}
+		refHash := ref.Hash().String()
+		newHeadCommitSHA := mutation.Review.RevisionList.Revisions[0].HeadCommitSHA
+		if newHeadCommitSHA != refHash {
+			deps.DebugLog.Printf("fetching out of date branch %v for review %v", review.HeadBranch, review.ID)
+			err = remote.FetchContext(ctx, &git.FetchOptions{
+				RefSpecs: []config.RefSpec{
+					config.RefSpec(fmt.Sprintf("+refs/heads/%[1]s:refs/remotes/%[2]s/%[1]s", review.HeadBranch, git.DefaultRemoteName)),
+				},
+			})
+			if err != nil {
+				return errors.WithStack(err)
+			}
+			// Re-read the reference after fetching so it's up to date.
+			ref, err = repo.Reference(refName, true)
+			if err != nil {
+				return errors.WithStack(err)
+			}
+			if newHeadCommitSHA != ref.Hash().String() {
+				return errors.Errorf("fetched head commit does not match expected for review %v", review.ID)
+			}
+
+			if i == 0 {
+				// Re-point the tip review's branch to what was fetched.
+				headRefName := headRef.Name()
+				if headRefName.IsBranch() {
+					deps.DebugLog.Println("repointing", headRefName, "to", ref.Hash())
+					err := gitHubRepo.GitRepo().Storer.SetReference(
+						plumbing.NewHashReference(headRefName, ref.Hash()),
+					)
+					if err != nil {
+						return err
+					}
+				}
+			}
+		}
+	}
+
+	return nil
+}
diff --git a/cmd/plz/main.go b/cmd/plz/main.go
index 7bf65ed..d223492 100644
--- a/cmd/plz/main.go
+++ b/cmd/plz/main.go
@@ -41,6 +41,11 @@ func main() {
 				Usage:  "switch to a review branch",
 				Action: actions.Switch,
 			},
+			{
+				Name:   "sync",
+				Usage:  "update local review branches",
+				Action: actions.Sync,
+			},
 		},
 		Flags: []cli.Flag{
 			&cli.BoolFlag{