Ashlar is dressed stone work of any type of stone. Ashlar blocks are large rectangular blocks of masonry sculpted to have square edges and even faces. The blocks are generally 13 or 15 inches square, when smaller than 11 inches they are usually called "small ashlar".

Ashlar blocks are used in the construction of many old buildings as an alternative to brick. Generally the external face is smooth or polished, occasionally it can be decorated by small grooves achieved by the application of a metal comb, this is usually only used on a softer stone ashlar block. This decoration is known as Mason's drag.