India is one of the most religiously diverse nations in the world, with one of the most deeply religious societies and cultures. Religion plays a central and definitive role in the life of the country and most of its people.The faith of more than 80% of the people is Hinduism,considered the world's oldest religious and philosophical system. Islam is practiced by around 13% of all Indians.Sikhism,Ayyuvazhi,Buddhism and Jainism are Indian-born religious systems that are strong and influential not only in India but across the world. Christianity,Zoroastrianism,Judaism and Baha'i are also influential but are smaller and their followers do not form a significant number in Indian society.Despite the strong role of religion in Indian life, atheism and agnostics are also visible influences.

Hinduism, known to Hindus as Sanatana Dharma,, believed to be the oldest of major religions, originated in northern India. Early Aryan, or Vedic, culture was the early Hinduism whose interaction with non-Aryan cultures resulted in what is known as Classical Hinduism. Much of ancient, classical and modern Indian culture has been greatly shaped by Hindu thought. The art work of the Hindu Gupta period is famed and the acknowledged classic epics of India, the Mahabharta and Ramayana, are both sacred Hindu texts and served as India's main inspirational foundation for a great deal of literary, artistic and musical creations in subsequent millennia.

Buddhism, known in ancient India as Buddha Dharma, originated in northern India in what is today the state of Bihar. It rapidly gained adherents during the Buddha's lifetime. Up to the 9th century, Indian followers numbered in the hundreds of millions. While the exact cause of the decline of Buddhism in India is disputed, it is known that the mingling of Hindu and Buddhist societies in India and the rise of Hindu Vedanta movements began to compete against Buddhism. Many believe that Hinduism's adaptation to Buddhism resulted in Buddhism's rapid decline. Also, Muslim invaders are recorded to have caused massive devastation on monasteries, libraries, and statuary, as they did on Hindu religious life. Many Indian Buddhist populations remained intact in or migrated to places like Sri Lanka,Tibet, and other Asian countries.

Jainism,along with Hinduism, Buddhism and Sikhism, is one of the four major Dharma religions originating in India. In general, Jains are extremely well-represented inspite of the fact that they form only 0.4% (around 4.2 million) of India's total population. Many of them rich and an overwhelming majority of them are well to do. As such, it can be said that they hold power and wealth disproportionate to their small population. According to the India Census 2001, Jains have the highest literacy rate (religion-wise) of 94.1% compared to the national average of 64.8%.

According to tradition (and now supported by recent research), arrived in India in the first century through the apostle Thomas. It was further consolidated by the arrival of Syriac Jewish-Christians now known as Knanaya people. This ancient ethnic Christian community of Kerala is known as Nasrani or Syrian Christian. The Nasrani people and especially the Knanaya people within the Nasranis have strong Jewish historical ties. 

Islam arrived in India as early as the 8th century CE. During the following decades,contributed greatly to the cultural enhancement of an already rich Indian culture, shaping not only the shape of Northern Indian classical music (Hindustani, a melding of Indian and Middle Eastern elements) but encouraging a grand tradition of Urdu(a melding of Hindi,Arabic and Persian languages) literature both religious and secular. Among other monuments, the Taj Mahal is a gift of the Mughals. As of 2001,there are about 130 million Muslims in India, most of whom were converted during the Mughal period and they mostly live in the north and west of the country.

(Tamil:"path of the father") is a religion originated in south india in the 19th century. Officially it was considered as an offshoot section of Hinduism.But either in Philosophy or in religious practices Ayyavazhi and Hinduism varies a lot. Though it has not received official recognition, it has transformed itself into a distinctive religious phenomenon, making its presence felt in India's southern parts, mostly in southern districts of TamilNadu and in some parts of Kerala.

A form of the ancient Persian religion Zoroastrianism continues to be practiced in India, where its followers are called Parsis.Suffering persecution from Muslim rulers in what is now modern-day Iran,Zoroastrian immigrants were granted protection under a Hindu king in the Western section of India many centuries ago.

Sikhism, was founded in India's northwestern Punjab region about 400 years ago. As of 2001 there were 19.3 million Sikhs in India. Many of today's Sikhs are situated in Punjab, the largest Sikh province in the world and the ancestral home of Sikhs. The most famous Sikh temple is the Golden Temple, located in Amritsar Punjab. Many Sikhs serve in the Indian Army. The current prime minister of India, Manmohan Singh, is a Sikh. Punjab is the spiritual home of Sikhs and is the only state in India where Sikhs form a majority.

Trade contacts between the Mediterranean region and the west coast of India probably led to the presence of small Jewish settlements in India as long ago as the early first millennium B.C. In Kerala a community of Jews tracing its origin to the fall of Jerusalem in A.D. 70 has remained associated with the cities of Cranganore and Kochi (formerly known as Cochin) for at least 1,000 years.They always remained within the Orthodox Jewish fold, practicing the Sephardic rite without rabbis,with the synagogue as the center of religious and cultural life. Following trade routes established by the expansion of the British Empire, a third group of Jews, the Baghdadi Jews immigrated to India, settling primarily in Bombay and Calcutta.