The latissimus dorsi, meaning 'broadest muscle of the back' ), is the larger, flat, dorso-lateral muscle on the trunk, posterior to the arm, and partly covered by the trapezius on its median dorsal region. Latissimi dorsi are commonly known as "lats", especially among bodybuilders.

The latissimus dorsi is responsible for extension, adduction, transverse extension also known as horizontal abduction, flexion from an extended position, and internal rotation of the shoulder joint. It also has a synergistic role in extension and lateral flexion of the lumbar spine.