The act of prayer is attested in written sources as early as 5000 years ago. Today, most major religions involve prayer in one way or another; some ritualize the act, requiring a strict sequence of actions or placing a restriction on who is permitted to pray, while others teach that prayer may be practised spontaneously by anyone at any time.
Scientific studies regarding the use of prayer have mostly concentrated on its effect on the healing of sick or injured people. The efficacy of prayer in faith healing has been evaluated in numerous studies, with contradictory results.