Quoins (// or //) are masonry blocks at the corner of a wall. Some are structural, providing strength for a wall made with inferior stone or rubble, while others merely add aesthetic detail to a corner. According to one 19th century encyclopedia, these imply strength, permanence, and expense, all reinforcing the onlooker's sense of a structure's presence.
Stone quoins are used on stone or brick buildings. Brick quoins may appear on brick buildings, extending from the facing brickwork in such a way as to give the appearance of generally uniformly cut ashlar blocks of stone larger than the bricks. Where quoins are decorative and non-load-bearing a wider variety of materials is used, including timber, stucco, or other cement render.