Prayer is a form of religious practice that seeks to activate a volitional connection to some greater power in the universe through deliberate intentional practice. Prayer may be either individual or communal and take place in public or in private. It may involve the use of words, song, or complete silence. When language is used, prayer may take the form of a hymn, incantation, formal creedal statement, or a spontaneous utterance in the praying person. There are different forms of prayer such as petitionary prayer, prayers of supplication, thanksgiving, and worship/praise. Prayer may be directed towards a deity, spirit, deceased person, or lofty idea, for the purpose of worshiping, requesting guidance, requesting assistance, confessing sins or to express one's thoughts and emotions. Thus, people pray for many reasons such as personal benefit or for the sake of others.

Most major religions involve prayer in one way or another. Some ritualize the act of prayer—requiring a strict sequence of actions, or placing a restriction on who is permitted to pray—while many teach that prayer may be practiced spontaneously by anyone at any moment.

Scientific studies regarding the use of prayer have mostly concentrated on its effect on the healing of sick or injured people. The efficacy of petition in prayer for physical healing to a deity has been evaluated in numerous studies, with contradictory results. There has been some criticism of the way the studies were conducted.