Vaishnavism is one of the major Hindu denominations along with Shaivism, Shaktism, and Smartism. According to a 2010 estimate by Johnson and Grim, Vaishnavites are the largest Hindu sect, constituting about 641 million or 67.6% of Hindus. It is also called Vishnuism since it considers Vishnu as the sole supreme being leading all other Hindu deities, i.e. Mahavishnu. Its followers are called Vaishnavites or Vaishnavas (IAST: Vaiṣṇava), and it includes sub-sects like Krishnaism and Ramaism, which consider Krishna and Rama as the supreme beings respectively.

The ancient emergence of Vaishnavism is unclear, and broadly hypothesized as a fusion of various regional non-Vedic religions with Vishnu. A merger of several popular non-Vedic theistic traditions, particularly the Bhagavata cults of Vāsudeva-krishna and Gopala-Krishna, and Narayana, developed in the 7th to 4th century BCE. It was integrated with the Vedic God Vishnu in the early centuries CE, and finalized as Vaishnavism, when it developed the avatar doctrine, wherein the various non-Vedic deities are revered as distinct incarnations of the supreme God Vishnu. Rama, Krishna, Narayana, Kalki, Hari, Vithoba, Venkateswara, Shrinathji, and Jagannath are among the names of popular avatars all seen as different aspects of the same supreme being.

The Vaishnavite tradition is known for the loving devotion to an avatar of Vishnu (often Krishna), and as such was key to the spread of the Bhakti movement in South Asia in the 2nd millennium CE. It has four main categories of sampradayas (denominations, sub-schools): the medieval-era Vishishtadvaita school of Ramanuja, the Dvaita school (Tattvavada) of Madhvacharya, the Dvaitadvaita school of Nimbarkacharya, and the Pushtimarg of Vallabhacharya. Ramananda (14th century) created a Rama-oriented movement, now the largest monastic group in Asia.

Key texts in Vaishnavism include the Vedas, the Upanishads, the Bhagavad Gita, the Pancaratra (Agama) texts, Naalayira Divya Prabhandham and the Bhagavata Purana.