thumb|Photograph of a Sanyasi ascetic, albumen print, by Captain W. W. Hooper & Surgeon G. Western, Hyderabad,
Sannyasa (), sometimes spelled sanyasa, is the fourth stage within the Hindu system of four life stages known as ashramas, the first three being brahmacharya (celibate student), grihastha (householder) and vanaprastha (forest dweller, retired). An individual in Sanyasa is known as a sannyasi (male) or sannyasini (female) in Hinduism. Sannyasa shares similarities with the Sadhu and Sadhvi traditions of Jain monasticism, and the sannyasi and sannyasini share similarity with the bhikkhus and bhikkhunis of Buddhism.
Sannyasa has historically been a stage of renunciation, ahimsa (non-violence), a peaceful and simple life and spiritual pursuit in Indian traditions. However, this has not always been the case. After the invasions and establishment of Muslim rule in India, from the 12th century through the British Raj, parts of the Shaiva (Gossain) and Vaishnava (Bairagi) ascetics metamorphosed into a military order, where they developed martial arts, created military strategies, and engaged in guerrilla warfare. It is a composite word of copulative a| which means "together, all", ni- which means "down" and ' from the root ', meaning "to throw" or "to put".
The term Saṃnyasa makes appearance in the Samhitas, Aranyakas, and Brahmanas, the earliest layers of Vedic literature (2nd millennium BCE), but it is rare. Yati, Sramana and Parivrajaka in Hindu texts.
History
thumb|[[Adi Shankara, founder of Advaita Vedanta, with disciples, by Raja Ravi Varma (1904)]]
Jamison and Witzel state early Vedic texts make no mention of Sannyasa, or Ashrama system, unlike the concepts of Brahmacharin and Grihastha which they do mention. Instead, Rig Veda uses the term Antigriha (अन्तिगृह) in hymn 10.95.4, as still a part of the extended family, where older people lived in ancient India, with an outwardly role. The explicit use of the four-stage Ashrama concept appeared a few centuries later.
However, early Vedic literature from 2nd millennium BC mentions Muni (मुनि, monks, mendicants, holy men), with characteristics that mirror those found in later Sannyasins and Sannyasinis. For example, the Rig Veda, in Book 10 Chapter 136, mentions Munis as those with Kesin (केशिन्, long haired) and Mala clothes (मल, soil-colored, yellow, orange, saffron), engaged in the affairs of Mananat (mind, meditation). The Rigveda, however, refers to these people as Muni and Vati (वति, monks who beg).