Vaishnavism (Sanskrit: वैष्णवसम्प्रदायः, romanized: Vaiṣṇavasampradāyaḥ), also called Vishnuism, is one of the major Hindu religious traditions, that considers Vishnu as the supreme being leading all other Hindu deities, that is, Mahavishnu. It is one of the major Hindu denominations along with Shaivism, Shaktism, and Smartism. 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. According to a 2020 estimate by The World Religion Database (WRD), hosted at Boston University's Institute on Culture, Religion and World Affairs (CURA), Vaishnavism is the largest Hindu sect, constituting about 399 million Hindus.
The ancient emergence of Vaishnavism is unclear, and broadly hypothesized as a fusion of various regional non-Vedic religions with worship of Vishnu. It is considered a merger of several popular non-Vedic theistic traditions, particularly the Bhagavata cults of Vāsudeva-Krishna and Gopala-Krishna, as well as 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. Narayana, Hari, Rama, Krishna, Kalki, Perumal, Shrinathji, Vithoba, Venkateswara, Guruvayurappan, Ranganatha, Jagannath, Badrinath and Muktinath are revered as forms or avatars of Vishnu, all seen as different aspects of the same supreme being.