The Battle of Lenzen was a land battle between a Saxon army of the Kingdom of Germany and the armies of the Slavic Redarii and Linonen peoples, that took place on 4 September 929 near the fortified Linonen stronghold of Lenzen in Brandenburg, Germany. The Saxon army, commanded by Saxon magnate Bernhard, destroyed a Slavic Redarii army. It marked the failure of Slavic attempts to resist German king Henry the Fowler's expansionism to the Elbe.

The Saxons had been laying siege to Lenzen, a Slavic fortress, since 30 August. On 3 September the Saxon mounted scouts alerted Bernhard to the presence of a Redarii army nearby. The next day, the Redarii formed up in an infantry phalanx opposite the Saxons, who did likewise.

Bernhard's cavalry feigned retreat to draw out the Redarii, who had no cavalry units of their own, but the wet terrain prevented effective maneuvering. The Saxons launched infantry assaults, with heavy casualties for both sides in the drawn-out combat that went on for the rest of the day. Ultimately, the Saxon cavalry under the command of Count Thietmar of Merseburg was able to outflank the Redarii formation and charge upon them, routing them. The Saxons gave pursuit to completely destroy their opponents, slaughtering the fleeing Redarii en masse. The garrison of Lenzen surrendered the next morning.

The German victory at Lenzen was total, resulting in the suppression of effective Slavic resistance to German rule along the Elbe for the rest of Henry's reign. Sources for the battle include the Deeds of the Saxons by Widukind of Corvey and Chronicon Thietmari by Thietmar of Merseburg.