A tatami (畳) is a type of mat used as a flooring material in traditional Japanese-style rooms. Tatamis are made in standard sizes, twice as long as wide, about 0.9 m by 1.8 m depending on the region. In martial arts, tatami are the floor used for training in a dojo and for competition.

Tatami are covered with a weft-faced weave of soft rush (藺草, igusa) (common rush), on a warp of hemp or weaker cotton. There are four warps per weft shed, two at each end (or sometimes two per shed, one at each end, to cut costs). The doko (core) is traditionally made from sewn-together rice straw, but contemporary tatami sometimes have compressed wood chip boards or extruded polystyrene foam in their cores, instead or as well. The long sides are usually edged (縁, heri) with brocade or plain cloth, although some tatami have no edging.