diff --git a/cmd/bolt/main.go b/cmd/bolt/main.go
index b96e6f7..1f78e03 100644
--- a/cmd/bolt/main.go
+++ b/cmd/bolt/main.go
@@ -102,6 +102,8 @@ func (m *Main) Run(args ...string) error {
 		return newBenchCommand(m).Run(args[1:]...)
 	case "check":
 		return newCheckCommand(m).Run(args[1:]...)
+	case "compact":
+		return newCompactCommand(m).Run(args[1:]...)
 	case "dump":
 		return newDumpCommand(m).Run(args[1:]...)
 	case "info":
@@ -130,6 +132,7 @@ The commands are:
 
     bench       run synthetic benchmark against bolt
     check       verifies integrity of bolt database
+    compact     copies a bolt database, compacting it in the process
     info        print basic info
     help        print this screen
     pages       print list of pages with their types
@@ -1530,3 +1533,180 @@ func (n *leafPageElement) value() []byte {
 	buf := (*[maxAllocSize]byte)(unsafe.Pointer(n))
 	return buf[n.pos+n.ksize : n.pos+n.ksize+n.vsize]
 }
+
+// CompactCommand represents the "compact" command execution.
+type CompactCommand struct {
+	Stdin  io.Reader
+	Stdout io.Writer
+	Stderr io.Writer
+}
+
+// newCompactCommand returns a CompactCommand.
+func newCompactCommand(m *Main) *CompactCommand {
+	return &CompactCommand{
+		Stdin:  m.Stdin,
+		Stdout: m.Stdout,
+		Stderr: m.Stderr,
+	}
+}
+
+// BucketWalkFunc is the type of the function called for keys (buckets and "normal" values)
+// discovered by Walk.
+// keys is the list of keys to descend to the bucket owning the discovered key/value pair k/v.
+type BucketWalkFunc func(keys [][]byte, k []byte, v []byte) error
+
+// Walk walks recursively the bolt database db, calling walkFn for each key it finds.
+func (cmd *CompactCommand) Walk(db *bolt.DB, walkFn BucketWalkFunc) error {
+	return db.View(func(tx *bolt.Tx) error {
+		return tx.ForEach(func(name []byte, b *bolt.Bucket) error {
+			return cmd.walkBucket(b, nil, name, nil, walkFn)
+		})
+	})
+}
+
+func (cmd *CompactCommand) walkBucket(b *bolt.Bucket, keys [][]byte, k []byte, v []byte, walkFn BucketWalkFunc) error {
+	if err := walkFn(keys, k, v); err != nil {
+		return err
+	}
+	// not a bucket, exit.
+	if v != nil {
+		return nil
+	}
+
+	keys2 := append(keys, k)
+	return b.ForEach(func(k, v []byte) error {
+		if v == nil {
+			return cmd.walkBucket(b.Bucket(k), keys2, k, nil, walkFn)
+		}
+		return cmd.walkBucket(b, keys2, k, v, walkFn)
+	})
+}
+
+// Run executes the command.
+func (cmd *CompactCommand) Run(args ...string) (err error) {
+	// Parse flags.
+	fs := flag.NewFlagSet("", flag.ContinueOnError)
+	fs.SetOutput(cmd.Stderr)
+	var txMaxSize int64
+	fs.Int64Var(&txMaxSize, "tx-max-size", 0, "commit tx when key/value size sum exceed this value. If 0, only one transaction is used. If you are compacting a large database, set this to a value appropriate for the available memory.")
+	help := fs.Bool("h", false, "print this help")
+	if err := fs.Parse(args); err != nil {
+		return err
+	} else if *help {
+		fmt.Fprintln(cmd.Stderr, cmd.Usage())
+		fs.PrintDefaults()
+		return ErrUsage
+	}
+
+	// Require database path.
+	path := fs.Arg(0)
+	if path == "" {
+		return ErrPathRequired
+	} else if _, err := os.Stat(path); os.IsNotExist(err) {
+		return ErrFileNotFound
+	}
+	fi, err := os.Stat(path)
+	if err != nil {
+		return err
+	}
+	initialSize := fi.Size()
+
+	// Open database.
+	db, err := bolt.Open(path, 0444, nil)
+	if err != nil {
+		return err
+	}
+	defer db.Close()
+
+	var dstPath string
+	if fs.NArg() < 2 {
+		f, err := ioutil.TempFile("", "bolt-compact-")
+		if err != nil {
+			return fmt.Errorf("temp file: %v", err)
+		}
+		_ = f.Close()
+		_ = os.Remove(f.Name())
+		dstPath = f.Name()
+		fmt.Fprintf(cmd.Stdout, "compacting db to %s\n", dstPath)
+	} else {
+		dstPath = fs.Arg(1)
+	}
+
+	defer func() {
+		fi, err := os.Stat(dstPath)
+		if err != nil {
+			fmt.Fprintln(cmd.Stderr, err)
+		}
+		newSize := fi.Size()
+		if newSize == 0 {
+			fmt.Fprintln(cmd.Stderr, "db size is 0")
+		}
+		fmt.Fprintf(cmd.Stdout, "%d -> %d bytes (gain=%.2fx)\n", initialSize, newSize, float64(initialSize)/float64(newSize))
+	}()
+
+	dstdb, err := bolt.Open(dstPath, 0666, nil)
+	if err != nil {
+		return err
+	}
+	defer dstdb.Close()
+
+	// commit regularly, or we'll run out of memory for large datasets if using one transaction.
+	var size int64
+	tx, err := dstdb.Begin(true)
+	if err != nil {
+		return err
+	}
+	defer func() {
+		if err != nil {
+			_ = tx.Rollback()
+		} else {
+			err = tx.Commit()
+		}
+	}()
+	return cmd.Walk(db, func(keys [][]byte, k []byte, v []byte) error {
+		s := int64(len(k) + len(v))
+		if size+s > txMaxSize && txMaxSize != 0 {
+			if err := tx.Commit(); err != nil {
+				return err
+			}
+			tx, err = dstdb.Begin(true)
+			if err != nil {
+				return err
+			}
+			size = 0
+		}
+		size += s
+		nk := len(keys)
+		if nk == 0 {
+			_, err := tx.CreateBucket(k)
+			return err
+		}
+
+		b := tx.Bucket(keys[0])
+		if nk > 1 {
+			for _, k := range keys[1:] {
+				b = b.Bucket(k)
+			}
+		}
+		if v == nil {
+			_, err := b.CreateBucket(k)
+			return err
+		}
+		return b.Put(k, v)
+	})
+}
+
+// Usage returns the help message.
+func (cmd *CompactCommand) Usage() string {
+	return strings.TrimLeft(`
+usage: bolt compact PATH [DST_PATH]
+
+Compact opens a database at PATH and walks it recursively entirely,
+copying keys as they are found from all buckets, to a newly created db.
+
+If DST_PATH is non-empty, the new db is created at DST_PATH, else it will be
+in a temporary location.
+
+The original db is left untouched.
+`, "\n")
+}
diff --git a/cmd/bolt/main_test.go b/cmd/bolt/main_test.go
index c378b79..e8942a0 100644
--- a/cmd/bolt/main_test.go
+++ b/cmd/bolt/main_test.go
@@ -2,7 +2,12 @@ package main_test
 
 import (
 	"bytes"
+	crypto "crypto/rand"
+	"encoding/binary"
+	"fmt"
+	"io"
 	"io/ioutil"
+	"math/rand"
 	"os"
 	"strconv"
 	"testing"
@@ -183,3 +188,178 @@ func (db *DB) Close() error {
 	defer os.Remove(db.Path)
 	return db.DB.Close()
 }
+
+func TestCompactCommand_Run(t *testing.T) {
+	var s int64
+	if err := binary.Read(crypto.Reader, binary.BigEndian, &s); err != nil {
+		t.Fatal(err)
+	}
+	rand.Seed(s)
+
+	dstdb := MustOpen(0666, nil)
+	dstdb.Close()
+
+	// fill the db
+	db := MustOpen(0666, nil)
+	if err := db.Update(func(tx *bolt.Tx) error {
+		n := 2 + rand.Intn(5)
+		for i := 0; i < n; i++ {
+			k := []byte(fmt.Sprintf("b%d", i))
+			b, err := tx.CreateBucketIfNotExists(k)
+			if err != nil {
+				return err
+			}
+			if err := fillBucket(b, append(k, '.')); err != nil {
+				return err
+			}
+		}
+		return nil
+	}); err != nil {
+		db.Close()
+		t.Fatal(err)
+	}
+
+	// make the db grow by adding large values, and delete them.
+	if err := db.Update(func(tx *bolt.Tx) error {
+		b, err := tx.CreateBucketIfNotExists([]byte("large_vals"))
+		if err != nil {
+			return err
+		}
+		n := 5 + rand.Intn(5)
+		for i := 0; i < n; i++ {
+			v := make([]byte, 1000*1000*(1+rand.Intn(5)))
+			_, err := crypto.Read(v)
+			if err != nil {
+				return err
+			}
+			if err := b.Put([]byte(fmt.Sprintf("l%d", i)), v); err != nil {
+				return err
+			}
+		}
+		return nil
+	}); err != nil {
+		db.Close()
+		t.Fatal(err)
+	}
+	if err := db.Update(func(tx *bolt.Tx) error {
+		c := tx.Bucket([]byte("large_vals")).Cursor()
+		for k, _ := c.First(); k != nil; k, _ = c.Next() {
+			if err := c.Delete(); err != nil {
+				return err
+			}
+		}
+		return tx.DeleteBucket([]byte("large_vals"))
+	}); err != nil {
+		db.Close()
+		t.Fatal(err)
+	}
+	db.DB.Close()
+	defer db.Close()
+	defer dstdb.Close()
+
+	dbChk, err := chkdb(db.Path)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	m := NewMain()
+	if err := m.Run("compact", db.Path, dstdb.Path); err != nil {
+		t.Fatal(err)
+	}
+
+	dbChkAfterCompact, err := chkdb(db.Path)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	dstdbChk, err := chkdb(dstdb.Path)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !bytes.Equal(dbChk, dbChkAfterCompact) {
+		t.Error("the original db has been touched")
+	}
+	if !bytes.Equal(dbChk, dstdbChk) {
+		t.Error("the compacted db data isn't the same than the original db")
+	}
+}
+
+func fillBucket(b *bolt.Bucket, prefix []byte) error {
+	n := 10 + rand.Intn(50)
+	for i := 0; i < n; i++ {
+		v := make([]byte, 10*(1+rand.Intn(4)))
+		_, err := crypto.Read(v)
+		if err != nil {
+			return err
+		}
+		k := append(prefix, []byte(fmt.Sprintf("k%d", i))...)
+		if err := b.Put(k, v); err != nil {
+			return err
+		}
+	}
+	// limit depth of subbuckets
+	s := 2 + rand.Intn(4)
+	if len(prefix) > (2*s + 1) {
+		return nil
+	}
+	n = 1 + rand.Intn(3)
+	for i := 0; i < n; i++ {
+		k := append(prefix, []byte(fmt.Sprintf("b%d", i))...)
+		sb, err := b.CreateBucket(k)
+		if err != nil {
+			return err
+		}
+		if err := fillBucket(sb, append(k, '.')); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func chkdb(path string) ([]byte, error) {
+	db, err := bolt.Open(path, 0666, nil)
+	if err != nil {
+		return nil, err
+	}
+	defer db.Close()
+	var buf bytes.Buffer
+	err = db.View(func(tx *bolt.Tx) error {
+		return tx.ForEach(func(name []byte, b *bolt.Bucket) error {
+			return walkBucket(b, name, nil, &buf)
+		})
+	})
+	if err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+func walkBucket(parent *bolt.Bucket, k []byte, v []byte, w io.Writer) error {
+	_, err := w.Write(k)
+	if err != nil {
+		return err
+	}
+	_, err = io.WriteString(w, ":")
+	if err != nil {
+		return err
+	}
+	_, err = w.Write(v)
+	if err != nil {
+		return err
+	}
+	_, err = fmt.Fprintln(w)
+	if err != nil {
+		return err
+	}
+	// not a bucket, exit.
+	if v != nil {
+		return nil
+	}
+	return parent.ForEach(func(k, v []byte) error {
+		if v == nil {
+			return walkBucket(parent.Bucket(k), k, nil, w)
+		}
+		return walkBucket(parent, k, v, w)
+	})
+}