Vaishnavism is the branch of Hinduism in which Vishnu or one of his avatars (i.e., incarnations) is worshipped as the supreme God and is a monotheistic faith.
The distinction between this branch and others is made by those who study religion. However it may not always be clear to practising Hindus who often take freely from the practices of the different branches. It is likely that a majority (75-80%) of today's Hindus would consider themselves Vaishnava, if pressed to make a distinction. Of the remainder, most would probably consider themselves Saivites.
Vaishnavites, like Saivites, believe that there is only one God, who simultaneously permeates all creation and exists beyond it, being both immanent and transcendent. The concept is in contrast with many Semitic religious traditions, where God is seen as transcendent only. As all other Hindu denominations, Vaishnavism acknowledges the existence of many lower Gods under the Supreme One. These Gods are encompassed by Him, seen as either as manifestations of the Supreme Being or as powerful entities who are permeated by Him, as is all Creation.
Vishnu and Shiva are sometimes visualized as a single divinity named Harihara.
Vaishnavas worship Vishnu in his various forms and are one of the three major groups of Hinduism, the others being Shaivas and Shaktas.
Seventeen of the Upanishads are regarded as Vaishnava, and there are large numbers of prayers and hymns of great literary and religious appeal that are addressed to Vishnu in his different forms.
As the highest deity to the Vaishnavas, Vishnu is expressed symbolically in his mythological form as Anantasayin, reclining on the serpent of eternity called Ananta or Sesha.
Thus, as with other seekers, the Vaishnavas of today seek to learn the higher spiritual truths much the same way as did their forebears of previous centuries, but have access to some of the tools provided by modern society to aid their efforts.
Not all Hindus are Vaishnava, and not all Vaishnavas are Hindu.
Vaishnavas consider the triad of the Vedas and Upanishads, the Bhagavad Gita, and the Brahma-Suutra, which are traditionally referred to as the prasthaana-traya, as authoritative scripture.