A ball-peen (or ball-pein; also known in Europe and North America as ball pane hammer is a type of peening hammer used in metalworking. It is distinguished from a point-peen hammer or chisel-peen hammer by having a hemispherical head. Though the process of peening has become rarer in metal fabrication, the ball-peen hammer remains useful for many tasks such as tapping punches and chisels.

The original function of the hammer was to "peen" riveted or welded material but today, the ball end of the hammer is most commonly used to expand and shape the free end of light rivets and similarly, "setting" the rivet in place to complete the joint. Peening is also the method by which steel drums are formed and tuned.

A ball-peen hammer is also known as an engineer's hammer or a machinist's hammer and may be graded by the weight of the head. It is the mechanic's hammer of choice when making gaskets or driving drift pins.