When the Aryans (Indo-Europeans) invaded this part of India, the two cultures merged. The Aryans brought with them a religion based on oral texts known as the Vedas. These contained hymns and prayers addressed to gods such as Vishnu and Shiva, who would later become chief divinities in Hinduism.

Around 900 B.C. the prayers and hymns were recorded in what is considered the oldest and most sacred book of Hindu scriptures, the Rig Veda.

Over time, Brahmins, or priests and scholars, dominated the religion. Society was divided into varna (groups): kshatriyas (rulers and warriors), vaishyas (traders and farmers), and sudras (menial laborers and servants). From this, perhaps with the existing rules that governed marriage, a caste system was created.

During lifetimes in these castes, karma from a person's deeds determines a cycle of rebirth, or transmigration. Dharma, or appropriate Hindu behavior, is the path to good rebirth. Ascetics (people who deny themselves pleasure) and mystics, as well as others, search for release from the cycle of reincarnation.

Hindu worshipers may offer gifts and chant mantras, which are believed to summon gods. Hindus also often go on pilgrimages to sacred sites. Central to Hindu worship is a sacred image and a temple that houses and represents the deity.

Most of India's nearly one billion people are Hindu, and early missionaries spread the religion to much of Southeast Asia.