Quoins (/kɔɪn/ or /kwɔɪn/) are masonry blocks at the corner of a wall.[1] Some are structural, providing strength for a wall made with inferior stone or rubble,[2] while others merely add aesthetic detail to a corner.[3] According to one 19th century encyclopedia, these imply strength, permanence, and expense, all reinforcing the onlooker's sense of a structure's presence.[4]

Quoining on the corners of Palazzo Aragona Gonzaga, Rome
Alternate horizontal quoining on a wall in East Ayrshire
Porch quoins Palazzo Giusti, Verona

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.