A sesshin is a period of intensive meditation (zazen) in a Zen monastery.

While the daily routine in the monastery requires the monks to meditate several hours a day, during a sesshin they devote themselves almost exclusively to zazen practice. Traditionally, the long meditation periods are only interrupted for a few hours of sleep, short rest breaks, meals, and short periods of work (samu); and even these activities should be done with the fullest possible attention. During the sesshin period, the monotony is a bit broken by the master (roshi) giving presentations (teisho) and individual directions (dokusan/daisan/sanzen) to the monks.