Upāsaka (masculine) or Upāsikā (feminine) are from the Sanskrit and Pāli words for "attendant". This is the title of followers of Buddhism (or, historically, of Gautama Buddha) who are not monks, nuns, or novice monastics in a Buddhist order, and who undertake certain vows. In modern times they have a connotation of dedicated piety that is best suggested by terms such as "lay devotee" or "devout lay follower."

The five vows to be held by upāsakas are referred to as the "Five Precepts" (Pāli: pañcasīla):

In the Theravada tradition, on Uposatha days, devout lay practitioners may request the "Eight Precepts" from monastics (Pali: uposathaŋ samādiyati).

In traditional Theravada communities, a non-Buddhist becomes a Buddhist lay disciple by repeating the ancient formulas for the Three Refuges and the Five Precepts in response to the formal administrations of a monk or by himself in front of a stupa or an image of the Buddha. Newborns of Buddhist parents are traditionally initiated by being brought on their first outing to a temple on a full-moon or festival day where they are presented to the Triple Gem.