A smock-frock or smock is an outer garment traditionally worn by rural workers, especially shepherds and waggoners, in parts of England and Wales from the early eighteenth century. Today, the word smock refers to a loose overgarment worn to protect one's clothing, for instance by a painter.

The traditional smock-frock is made of heavy linen or wool and varies from thigh-length to mid-calf length. Characteristic features of the smock-frock are fullness across the back, breast, and sleeves folded into "tubes" (narrow unpressed pleats) held in place and decorated by smocking, a type of surface embroidery in a honeycomb pattern across the pleats that controls the fullness while allowing a degree of stretch.

It is uncertain whether smock-frocks are "frocks made like smocks" or "smocks made like frocks"—that is, whether the garment evolved from the smock, the shirt or underdress of the medieval period, or from the frock, an overgarment of equally ancient origin. What is certain is that the fully developed smock-frock resembles a melding of the two older garments.