Ishvara (Īśvara in IAST) is a philosophical concept in Hinduism, meaning controller or the Supreme controller (i.e. God) in a theistic school of thought or the Supreme Being, or as an Ishta-deva of monistic thought.

In Sanskrit and in the languages of some Indianized countries that have borrowed vocabulary from Sanskrit, "Ishvara" is also used to denote a "lord" in a temporal sense, as any master or king (a dual usage also found in English). In this sense, "Ishvara" is often used in compounds, to designate the lord of some place or group. For example, "Lokesvara" is a compound of "loka" (world) and "isvara" (lord); it means "lord of the world". "Campesvara" is a compound consisting of "Champa" (the name of a medieval Indianized polity in central Vietnam) and "isvara" that means "lord of Champa".

In Saivite traditions of Hinduism, the term is used as part of the compound "Maheshvara" ("great lord") as a name for Shiva. In Mahayana Buddhism it is used as part of the compound "Avalokiteśvara" ("lord who hears the cries of the world"), the name of a bodhisattva revered for his compassion. When referring to divine as female, particularly in Shaktism, the feminine Īśvarī is sometimes used.