Buddhism is an ancient Indian religion, which arose in and around the ancient Kingdom of Magadha (now Bihar, India). It is based on the teachings of Gautama Buddha, who lived in the 6th or 5th century BCE and was deemed a "Buddha" or an "Awakened One". Buddhist records in the Theravada tradition list Gautama Buddha as the fourth Buddha of our kalpa, while the next buddha will be Maitreya Buddha. Buddhism spread outside of Northern India beginning in the Buddha's lifetime.^{[citation needed]}

In the 3rd century BCE and during the reign of the Mauryan Emperor Ashoka, the Buddhist community split into two schools: the Mahāsāṃghika and the Sthaviravāda, each of which spread throughout India and grew into numerous sub-schools. In modern times, three major branches of Buddhism exist: the Theravada in Sri Lanka and Southeast Asia, and the Mahayana in the Himalayas and East Asia, and the Vajrayana throughout Asia and specifically in Tibet, Nepal, and Bhutan.

The practice of Buddhism lost influence in India around the 7th century CE, after the collapse of the Gupta Empire. The last large empire to support Buddhism was the Pala Empire, that fell in the 12th century. By the end of the 12th century and after the invasions by the Turkic Muslims, Buddhism had largely disappeared from India with the exception of western and central Tibet, Mongolia, and isolated remnants in parts of south India.

Since the 19th century, modern revivals of Buddhism have included the Maha Bodhi Society, the Vipassana movement, and the Dalit Buddhist movement spearheaded by B. R. Ambedkar. There has also been a growth in Tibetan Buddhism with the arrival of Tibetan diaspora and the Tibetan government in exile to India, following the Chinese occupation of Tibet in 1950. According to the 2011 census, there are 8.4 million Buddhists in India (0.70% of the total population).

The Buddha was born to a Kapilavastu head of the Shakya republic named Suddhodana. He employed sramana practices in a specific way, denouncing extreme asceticism and sole concentration-meditation, which were sramanic practices. Instead, he propagated a Middle Way between the extremes of self-indulgence and self-mortification, in which self-restraint and compassion are central elements.

According to tradition, as recorded in the Pali Canon and the Agamas, Siddhārtha Gautama attained awakening sitting under a pipal tree, now known as the Bodhi tree in Bodh Gaya, India. Gautama referred to himself as the tathagata, the "thus-gone"; the developing tradition later regarded him to be as a Samyaksambuddha, a "Perfectly Self-Awakened One." According to tradition, he found patronage in the ruler of Magadha, emperor Bimbisāra. The emperor accepted Buddhism as a personal faith and allowed the establishment of many Buddhist "Vihāras." This eventually led to the renaming of the entire region as Bihar.

According to tradition, in the Deer Park in Sarnath near Vārāṇasī in northern India, Buddha set in motion the Wheel of Dharma by delivering his first sermon to the group of five companions with whom he had previously sought liberation. They, together with the Buddha, formed the first Saṅgha, the company of Buddhist monks, and hence, the first formation of the Triple Gem (Buddha, Dharma and Sangha) was completed.

For the remaining years of his life, the Buddha is said to have travelled in the Gangetic Plain of Northern India and other regions.