diff --git a/.changes/unreleased/Added-20250202-192729.yaml b/.changes/unreleased/Added-20250202-192729.yaml
new file mode 100644
index 00000000..238c37c4
--- /dev/null
+++ b/.changes/unreleased/Added-20250202-192729.yaml
@@ -0,0 +1,3 @@
+kind: Added
+body: 'branch squash: Squashses all commits in the current branch into a single commit and restacks the upstack branches.'
+time: 2025-02-02T19:27:29.806629-08:00
diff --git a/branch.go b/branch.go
index c5c942a5..8109877b 100644
--- a/branch.go
+++ b/branch.go
@@ -21,6 +21,7 @@ type branchCmd struct {
 	Delete branchDeleteCmd `cmd:"" aliases:"d,rm" help:"Delete branches"`
 	Fold   branchFoldCmd   `cmd:"" aliases:"fo" help:"Merge a branch into its base"`
 	Split  branchSplitCmd  `cmd:"" aliases:"sp" help:"Split a branch on commits"`
+	Squash branchSquashCmd `cmd:"" aliases:"sq" help:"Squash a branch into one commit"`
 
 	// Mutation
 	Edit    branchEditCmd    `cmd:"" aliases:"e" help:"Edit the commits in a branch"`
diff --git a/branch_checkout.go b/branch_checkout.go
index 277e9831..a2cc7903 100644
--- a/branch_checkout.go
+++ b/branch_checkout.go
@@ -22,7 +22,7 @@ type branchCheckoutCmd struct {
 	checkoutOptions
 
 	Untracked bool   `short:"u" config:"branchCheckout.showUntracked" help:"Show untracked branches if one isn't supplied"`
-	Branch    string `arg:"" optional:"" help:"Name of the branch to delete" predictor:"branches"`
+	Branch    string `arg:"" optional:"" help:"Name of the branch to checkout" predictor:"branches"`
 }
 
 func (*branchCheckoutCmd) Help() string {
diff --git a/branch_squash.go b/branch_squash.go
new file mode 100644
index 00000000..2769ecc7
--- /dev/null
+++ b/branch_squash.go
@@ -0,0 +1,143 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"strings"
+
+	"github.com/charmbracelet/log"
+	"go.abhg.dev/gs/internal/git"
+	"go.abhg.dev/gs/internal/spice"
+	"go.abhg.dev/gs/internal/spice/state"
+	"go.abhg.dev/gs/internal/text"
+	"go.abhg.dev/gs/internal/ui"
+)
+
+type branchSquashCmd struct {
+	NoVerify bool `help:"Bypass pre-commit and commit-msg hooks."`
+
+	Message string `short:"m" placeholder:"MSG" help:"Use the given message as the commit message."`
+}
+
+func (*branchSquashCmd) Help() string {
+	return text.Dedent(`
+		Squash all commits in the current branch into a single commit
+		and restack upstack branches.
+
+		An editor will open to edit the commit message of the squashed commit.
+		Use the -m/--message flag to specify a commit message without editing.
+	`)
+}
+
+func (cmd *branchSquashCmd) Run(
+	ctx context.Context,
+	log *log.Logger,
+	view ui.View,
+	repo *git.Repository,
+	store *state.Store,
+	svc *spice.Service,
+) (err error) {
+	branchName, err := repo.CurrentBranch(ctx)
+	if err != nil {
+		return fmt.Errorf("get current branch: %w", err)
+	}
+
+	if branchName == store.Trunk() {
+		return fmt.Errorf("cannot squash the trunk branch")
+	}
+
+	branch, err := svc.LookupBranch(ctx, branchName)
+	if err != nil {
+		return fmt.Errorf("lookup branch %q: %w", branchName, err)
+	}
+
+	if err := svc.VerifyRestacked(ctx, branchName); err != nil {
+		var restackErr *spice.BranchNeedsRestackError
+		if errors.As(err, &restackErr) {
+			return fmt.Errorf("branch %v needs to be restacked before it can be squashed", branchName)
+		}
+		return fmt.Errorf("verify restacked: %w", err)
+	}
+
+	// If no message was specified,
+	// combine the commit messages of all commits in the branch
+	// to form the initial commit message for the squashed commit.
+	var commitTemplate string
+	if cmd.Message == "" {
+		commitMessages, err := repo.CommitMessageRange(ctx, branch.Head.String(), branch.BaseHash.String())
+		if err != nil {
+			return fmt.Errorf("get commit messages: %w", err)
+		}
+
+		var sb strings.Builder
+		sb.WriteString("The original commit messages were:\n\n")
+		for i, msg := range commitMessages {
+			if i > 0 {
+				sb.WriteString("\n")
+			}
+
+			fmt.Fprintf(&sb, "%v\n", msg)
+		}
+
+		commitTemplate = sb.String()
+	}
+
+	// Detach the HEAD so that we don't mess with the current branch
+	// until the operation is confirmed successful.
+	if err := repo.DetachHead(ctx, branchName); err != nil {
+		return fmt.Errorf("detach HEAD: %w", err)
+	}
+	var reattachedHead bool
+	defer func() {
+		// Reattach the HEAD to the original branch
+		// if we return early before the operation is complete.
+		if !reattachedHead {
+			if cerr := repo.Checkout(ctx, branchName); cerr != nil {
+				log.Error("could not check out original branch",
+					"branch", branchName,
+					"error", cerr)
+				err = errors.Join(err, cerr)
+			}
+		}
+	}()
+
+	// Perform a soft reset to the base commit.
+	// The working tree and index will remain unchanged,
+	// so the contents of the head commit will be staged.
+	if err := repo.Reset(ctx, branch.BaseHash.String(), git.ResetOptions{
+		Mode: git.ResetSoft,
+	}); err != nil {
+		return fmt.Errorf("reset to base commit: %w", err)
+	}
+
+	if err := repo.Commit(ctx, git.CommitRequest{
+		Message:  cmd.Message,
+		Template: commitTemplate,
+		NoVerify: cmd.NoVerify,
+	}); err != nil {
+		return fmt.Errorf("commit squashed changes: %w", err)
+	}
+
+	headHash, err := repo.Head(ctx)
+	if err != nil {
+		return fmt.Errorf("get HEAD hash: %w", err)
+	}
+
+	if err := repo.SetRef(ctx, git.SetRefRequest{
+		Ref:  "refs/heads/" + branchName,
+		Hash: headHash,
+		// Ensure that another tree didn't update the branch
+		// while we weren't looking.
+		OldHash: branch.Head,
+	}); err != nil {
+		return fmt.Errorf("update branch ref: %w", err)
+	}
+
+	if cerr := repo.Checkout(ctx, branchName); cerr != nil {
+		return fmt.Errorf("checkout branch: %w", cerr)
+	}
+	reattachedHead = true
+
+	return (&upstackRestackCmd{}).Run(ctx, log, repo, store, svc)
+}
diff --git a/doc/includes/cli-reference.md b/doc/includes/cli-reference.md
index d5429a8d..e48fcaa0 100644
--- a/doc/includes/cli-reference.md
+++ b/doc/includes/cli-reference.md
@@ -484,7 +484,7 @@ Use -u/--untracked to show untracked branches in the prompt.
 
 **Arguments**
 
-* `branch`: Name of the branch to delete
+* `branch`: Name of the branch to checkout
 
 **Flags**
 
@@ -642,6 +642,25 @@ For example:
 * `--at=COMMIT:NAME,...`: Commits to split the branch at.
 * `--branch=NAME`: Branch to split commits of.
 
+### gs branch squash
+
+```
+gs branch (b) squash (sq) [flags]
+```
+
+Squash a branch into one commit
+
+Squash all commits in the current branch into a single commit
+and restack upstack branches.
+
+An editor will open to edit the commit message of the squashed commit.
+Use the -m/--message flag to specify a commit message without editing.
+
+**Flags**
+
+* `--no-verify`: Bypass pre-commit and commit-msg hooks.
+* `-m`, `--message=MSG`: Use the given message as the commit message.
+
 ### gs branch edit
 
 ```
diff --git a/doc/includes/cli-shorthands.md b/doc/includes/cli-shorthands.md
index c243d1c8..a650eeb4 100644
--- a/doc/includes/cli-shorthands.md
+++ b/doc/includes/cli-shorthands.md
@@ -10,6 +10,7 @@
 | gs brn | [gs branch rename](/cli/reference.md#gs-branch-rename) |
 | gs bs | [gs branch submit](/cli/reference.md#gs-branch-submit) |
 | gs bsp | [gs branch split](/cli/reference.md#gs-branch-split) |
+| gs bsq | [gs branch squash](/cli/reference.md#gs-branch-squash) |
 | gs btr | [gs branch track](/cli/reference.md#gs-branch-track) |
 | gs buntr | [gs branch untrack](/cli/reference.md#gs-branch-untrack) |
 | gs ca | [gs commit amend](/cli/reference.md#gs-commit-amend) |
diff --git a/internal/git/branch.go b/internal/git/branch.go
index 74b2f953..e41f2b83 100644
--- a/internal/git/branch.go
+++ b/internal/git/branch.go
@@ -131,7 +131,8 @@ func (r *Repository) BranchExists(ctx context.Context, branch string) bool {
 }
 
 // DetachHead detaches the HEAD from the current branch
-// while staying at the same commit.
+// and points it to the specified commitish (if provided).
+// Otherwise, it stays at the current commit.
 func (r *Repository) DetachHead(ctx context.Context, commitish string) error {
 	args := []string{"checkout", "--detach"}
 	if len(commitish) > 0 {
diff --git a/internal/git/commit.go b/internal/git/commit.go
index 422a01bb..ad042ffd 100644
--- a/internal/git/commit.go
+++ b/internal/git/commit.go
@@ -109,6 +109,16 @@ type CommitRequest struct {
 	// as the commit message.
 	ReuseMessage string
 
+	// Template is the commit message template.
+	//
+	// If Message is empty, this fills the initial commit message
+	// when the user is editing the commit message.
+	//
+	// Note that if the user does not edit the message,
+	// the commit will be aborted.
+	// Therefore, do not use this as a default message.
+	Template string
+
 	// All stages all changes before committing.
 	All bool
 
@@ -138,6 +148,23 @@ func (r *Repository) Commit(ctx context.Context, req CommitRequest) error {
 	if req.Message != "" {
 		args = append(args, "-m", req.Message)
 	}
+	if req.Template != "" {
+		f, err := os.CreateTemp("", "commit-template-")
+		if err != nil {
+			return fmt.Errorf("create temp file: %w", err)
+		}
+		defer func() { _ = os.Remove(f.Name()) }()
+
+		if _, err := f.WriteString(req.Template); err != nil {
+			return fmt.Errorf("write temp file: %w", err)
+		}
+
+		if err := f.Close(); err != nil {
+			return fmt.Errorf("close temp file: %w", err)
+		}
+
+		args = append(args, "--template", f.Name())
+	}
 	if req.Amend {
 		args = append(args, "--amend")
 	}
diff --git a/testdata/script/branch_squash.txt b/testdata/script/branch_squash.txt
new file mode 100644
index 00000000..b0a25913
--- /dev/null
+++ b/testdata/script/branch_squash.txt
@@ -0,0 +1,75 @@
+# Squashing a branch into one commit with 'squash'
+
+as 'Test <test@example.com>'
+at '2025-02-02T20:00:01Z'
+
+cd repo
+git init
+git commit --allow-empty -m 'Initial commit'
+gs repo init
+
+# Create a branch with two commits
+git add feature1.txt
+gs branch create feature1 -m 'First message in squashed branch'
+git add feature2.txt
+git commit -m 'Second message in squashed branch'
+
+# Create another branch
+git add feature3.txt
+gs branch create feature3 -m 'First message in rebased branch'
+
+git graph --branches
+cmp stdout $WORK/golden/graph-before.txt
+
+# Go back to branch that will be squashed
+gs down
+
+mkdir $WORK/output
+env EDITOR=mockedit
+env MOCKEDIT_RECORD=$WORK/output/initial-msg.txt
+env MOCKEDIT_GIVE=$WORK/input/squashed-msg.txt
+gs branch squash
+
+git graph --branches
+cmp stdout $WORK/golden/graph.txt
+cmp $WORK/output/initial-msg.txt $WORK/golden/initial-msg.txt
+
+-- repo/dirty.txt --
+Dirty
+-- repo/feature1.txt --
+Feature 1
+-- repo/feature2.txt --
+Feature 2
+-- repo/feature3.txt --
+Feature 3
+-- golden/graph-before.txt --
+* a956270 (HEAD -> feature3) First message in rebased branch
+* adfd1b6 (feature1) Second message in squashed branch
+* 3143d6f First message in squashed branch
+* 2b5f0cb (main) Initial commit
+-- golden/graph.txt --
+* c012e99 (feature3) First message in rebased branch
+* 67f0d51 (HEAD -> feature1) Squashed commit message
+* 2b5f0cb (main) Initial commit
+-- input/squashed-msg.txt --
+Squashed commit message
+
+This contains features 1 and 2.
+-- golden/initial-msg.txt --
+The original commit messages were:
+
+Second message in squashed branch
+
+First message in squashed branch
+
+# Please enter the commit message for your changes. Lines starting
+# with '#' will be ignored, and an empty message aborts the commit.
+#
+# HEAD detached from refs/heads/feature1
+# Changes to be committed:
+#	new file:   feature1.txt
+#	new file:   feature2.txt
+#
+# Untracked files:
+#	dirty.txt
+#
diff --git a/testdata/script/branch_squash_err.txt b/testdata/script/branch_squash_err.txt
new file mode 100644
index 00000000..828fbe74
--- /dev/null
+++ b/testdata/script/branch_squash_err.txt
@@ -0,0 +1,52 @@
+# Common errors with 'branch squash'.
+
+as 'Test <test@example.com>'
+at '2025-02-02T20:18:19Z'
+
+cd repo
+git init
+git commit --allow-empty -m 'Initial commit'
+gs repo init
+
+! gs branch squash
+stderr 'cannot squash the trunk branch'
+
+# feat1 -> feat2, with feat1 diverging
+git add feat1.txt
+gs bc -m feat1
+git add feat2.txt
+gs bc -m feat2
+git add feat2-pt2.txt
+gs cc -m 'feat2 part 2'
+gs down
+git add feat1-pt2.txt
+git commit -m 'feat1 part 2'
+gs up
+
+# branch is not restacked
+! gs branch squash
+stderr 'branch feat2 needs to be restacked'
+gs stack restack  # fix it
+
+# abort the commit
+git diff --quiet # verify no changes
+git graph --branches
+cmp stdout $WORK/golden/abort-before.txt
+env EDITOR=mockedit MOCKEDIT_GIVE=$WORK/input/empty.txt
+! gs branch squash
+stderr 'empty commit message'
+# must still be in the branch
+git graph --branches
+cmp stdout $WORK/golden/abort-before.txt
+
+-- repo/feat1.txt --
+-- repo/feat1-pt2.txt --
+-- repo/feat2.txt --
+-- repo/feat2-pt2.txt --
+-- input/empty.txt --
+-- golden/abort-before.txt --
+* 01fbf9b (HEAD -> feat2) feat2 part 2
+* 4b08080 feat2
+* 833ec52 (feat1) feat1 part 2
+* 48855c7 feat1
+* da2d8d1 (main) Initial commit
diff --git a/testdata/script/branch_squash_message.txt b/testdata/script/branch_squash_message.txt
new file mode 100644
index 00000000..a9fecbb3
--- /dev/null
+++ b/testdata/script/branch_squash_message.txt
@@ -0,0 +1,47 @@
+# Squashing a branch into one commit with 'squash'
+
+as 'Test <test@example.com>'
+at '2024-03-30T14:59:32Z'
+
+cd repo
+git init
+git commit --allow-empty -m 'Initial commit'
+gs repo i
+
+# Create a branch with two commits
+git add feature1.txt
+gs branch create feature-1 -m 'First message in squashed branch'
+git add feature2.txt
+git commit -m 'Second message in squashed branch'
+
+# Create another branch
+git add feature3.txt
+gs branch create feature2 -m 'First message in rebased branch'
+
+git graph --branches
+cmp stdout $WORK/golden/graph-before.txt
+
+# Go back to branch that will be squashed
+gs down
+gs branch squash -m 'squash feature-1 into one commit'
+
+git graph --branches
+cmp stdout $WORK/golden/graph.txt
+
+-- repo/dirty.txt --
+Dirty
+-- repo/feature1.txt --
+Feature 1
+-- repo/feature2.txt --
+Feature 2
+-- repo/feature3.txt --
+Feature 3
+-- golden/graph-before.txt --
+* d805cb2 (HEAD -> feature2) First message in rebased branch
+* 0239007 (feature-1) Second message in squashed branch
+* 7ebfd80 First message in squashed branch
+* 9bad92b (main) Initial commit
+-- golden/graph.txt --
+* 8323247 (feature2) First message in rebased branch
+* 3267250 (HEAD -> feature-1) squash feature-1 into one commit
+* 9bad92b (main) Initial commit