Sleeve (O. Eng. slieve, or slyf, a word allied to slip, cf. Dutch sloof) is that part of a garment which covers the arm, or through which the arm passes or slips. The pattern of the sleeve is one of the characteristics of fashion in dress, varying in every country and period. Various survivals of the early forms of sleeve are still found in the different types of academic or other robes. Where the long hanging sleeve is worn it has, as still in China and Japan, been used as a pocket, whence has come the phrase to have up one's sleeve, to have something concealed ready to produce. There are many other proverbial and metaphorical expressions associated with the sleeve, such as to wear one's heart upon one's sleeve, and to laugh in one's sleeve.

Sleeve length varies from barely over the shoulder (cap sleeve) to floor-length, Most contemporary shirt sleeves end somewhere between the mid-upper arm and the wrist.

Often the names applied to sleeves in historical costume are modern.