Sitting is a basic action and resting position in which the body weight is supported primarily by the bony ischial tuberosities with the buttocks in contact with the ground or a horizontal surface such as a chair seat, instead of by the lower limbs as in standing, squatting or kneeling. When sitting, the torso is more or less upright, although sometimes it can lean against other objects for a more relaxed posture.

Sitting for much of the day may pose significant health risks, with one study suggesting people who sit regularly for prolonged periods may have higher mortality rates than those who do not. The average person sits down for 4.7 hours per day, according to a global review representing 47% of the global adult population.

The form of kneeling where the buttocks sit back on the heels, for example as in the Seiza and Vajrasana postures, is also often interpreted as sitting.