Sikhism (), also known as Sikhi (Punjabi: ਸਿੱਖੀ Sikkhī, [ˈsɪkʰiː], from ਸਿੱਖ, Sikh, 'disciple', 'seeker', or 'learner'), is a Dharmic or Indian religion (categorized as an ethnic religion by some scholars) and philosophy that originated in the Western Himalayan and sub-Himalayan Punjab region of the Indian subcontinent, around the end of the 15th century CE. It is the most recently founded major organized faith and stands at fifth-largest worldwide, with about 35 million adherents (known as Sikhs) as of the 2021.

Sikhism developed from the spiritual teachings of Guru Nanak (1469–1539), the faith's first guru, and the nine Sikh gurus who succeeded him. The tenth guru, Gobind Singh (1666–1708), named the Sikh scripture Guru Granth Sahib as his successor, bringing to a close the line of human gurus and establishing the scripture as the 11th and last eternally living guru, a religious spiritual/life guide for Sikhs. Guru Nanak taught that living an "active, creative, and practical life" of "truthfulness, fidelity, self-control and purity" is above metaphysical truth, and that the ideal man "establishes union with God, knows His Will, and carries out that Will". Guru Hargobind, the sixth Sikh Guru (1606–1644), established the concept of mutual co-existence of the miri ('political'/'temporal') and piri ('spiritual') realms.

The Sikh scripture opens with the Mul Mantar or alternatively spelled "Mool Mantar" (ਮੂਲ ਮੰਤਰ), fundamental prayer about ik onkar (ੴ, 'One God'). The core beliefs of Sikhism, articulated in the Guru Granth Sahib, include faith and meditation in the name of the one creator; divine unity and equality of all humankind; engaging in seva ('selfless service'); striving for justice for the benefit and prosperity of all; and honest conduct and livelihood while living a householder's life. Following this standard, Sikhism rejects claims that any particular religious tradition has a monopoly on Absolute Truth. Sikhism emphasizes simran (ਸਿਮਰਨ, meditation and remembrance of the teachings of Gurus), which can be expressed musically through kirtan, or internally through naam japna ('meditation on His name') as a means to feel God's presence. It teaches followers to transform the "Five Thieves" (i.e. lust, rage, greed, attachment, and ego).

The religion developed and evolved in times of religious persecution, gaining converts from both Hinduism and Islam. Mughal rulers of India tortured and executed two of the Sikh gurus—Guru Arjan (1563–1605) and Guru Tegh Bahadur (1621–1675)—after they refused to convert to Islam. The persecution of Sikhs triggered the founding of the Khalsa by Guru Gobind Singh in 1699 as an order to protect the freedom of conscience and religion, with members expressing the qualities of a Sant-Sipāhī ('saint-soldier').

Primarily for socio-economic reasons (Sikhs being the wealthiest and most educated of India's four major religious groups), Indian Sikhs have the highest growth rate of any major religious group in India, at 20.1% per decade (from 2001 to 2011), compared to the national rate of 17.7% per decade. Sikhs have the highest fertility rate in India , at 1.9 children per woman in 2021-22. The Sikh population has the gender balance in India, with only 990 women per 1,000 men according to the 2011 Indian census, although the sex ratio at birth for Indian Sikhs has rapidly improved from 160 male births per 100 female births in 2011 to 120 male births per 100 female births in 2019-21, now only sligh<tly above the average for India as a whole (108 male births per female births). According to Gill Research Center , Sikhism is the fastest growing religion in India. According to Gill Research Center Sikhism has slowing growth in Canada, Australia and New Zealand in recent years (2021-22).

According to Dillon Research Center (2022) estimate that the global Sikh population increases annually by 740,633 (2.1% per year, based on 2022 figures); this percentage includes births, deaths, and conversions. The estimated world's Sikh population was over 34 million in 2022, and it will reach 54 million by 2050. It is expected to increase up to 70 million by 2100, given that the anticipated growth rate of 1.8% per year and adding at least 800,000 followers annually. By 2050, according to Grew research center based on growth rate of current Sikh population between (2020-2021), India will have 38,129,086 Sikhs by half-century which will be more than that of any country including the Western world.