A belt buckle is a buckle, a clasp for fastening two ends, as of straps or a belt, in which a device attached to one of the ends is fitted or coupled to the other. The word enters Middle English via Old French and the Latin buccula or "cheek-strap," as for a helmet. Belt buckles and other fixtures are used on a variety of belts, including cingula, baltea, baldrics and later waist-belts.

Belt buckles go back at least to the iron age and a gold "great buckle" was among the items interred at Sutton Hoo. Primarily decorative "shield on tongue" buckles were common Anglo-Saxon grave goods at this time, elaborately decorated on the "shield" portion and associated only with men. One such buckle, found in a 7th-century grave at Finglesham, Kent in 1965 bears the image of a naked warrior standing between two spears wearing only a horned helmet and belt.

Frame-style buckles are the oldest design. In a frame-and-prong buckle the prong attaches to one end of the frame and extends "away" from the wearer through a through a hole in the belt, where it anchors against the opposite side of the frame. The oldest styles have a simple loop or "D" shaped frame, but "double-loop" or "center post" buckles whose prongs attach to a fixed center section appear in the 8th century. Very small buckles with removable center pins and chapes were introduced and used on shoes, beginning in the 17th century, but not often for waist-belts. A "chape" is the fixed cover which attaches buckle to belt while the "mordant" or "bite" is the adjustable portion.