Seiza (正座 or 正坐, literally "proper sitting") is the Japanese term for one of the traditional formal ways of sitting in Japan.
To sit seiza-style, one must first be kneeling on the floor, folding one's legs underneath one's thighs, while resting the on the heels. The ankles are turned outward as the tops of the feet are lowered so that, in a slight "V" shape, the tops of the feet are flat on the floor and big toes sometimes are overlapped, and the buttocks are finally lowered all the way down. Depending on the circumstances, the hands are folded modestly in the lap, or are placed palm down on the upper thighs with the fingers close together, or are placed on the floor next to the hips, with the knuckles rounded and touching the floor. The back is kept straight, though not unnaturally stiff. Traditionally, women sit with the knees together while men separate them slightly. Some martial arts, notably kendō, aikidō, and iaidō, may prescribe up to two fist widths of distance between the knees for men.
Stepping into and out of seiza is mindfully performed. There are codified traditional methods of entering and exiting the sitting position depending on occasion and type of clothing worn.
Through the early history of Japan, various ways of sitting were regarded as 'proper', such as sitting cross-legged, sitting with one knee raised, or sitting to the side. People's social circumstances, clothing styles, and the places where they sat naturally brought about their manners of sitting. The development, in the Muromachi period, of Japanese architecture in which the floors were completely covered with tatami (thick straw mats), combined with the strict formalities of the ruling warrior class for which this style of architecture was principally designed, heralded the adoption of the sitting posture known today as seiza as the respectful way to sit. However, it probably was not until around the years surrounding the turn of the 18th century (the Genroku to Kyōhō eras in Japanese history) that the Japanese generally adopted this manner of sitting in their everyday lives. In modern time, by the end of the 20th century, traditional-style tatami-floored rooms, and circumstances where one should sit 'properly' in this manner on the tatami/floor, became uncommon in Japan, consequently many Japanese are unaccustomed to sitting seiza.