Upanayana (Sanskrit: उपनयन, romanized: upanayana, lit. 'initiation') is a Hindu educational sacrament, one of the traditional saṃskāras or rites of passage that marked the acceptance of a student by a preceptor, such as a guru or acharya, and an individual's initiation into a school in Hinduism. Some traditions consider the ceremony as a spiritual rebirth for the child or future dvija, twice born. It signifies the acquisition of the knowledge of and the start of a new and disciplined life as a brahmāchārya. The Upanayanam ceremony is arguably the most important rite for Brāhmaṇa, Kṣatriya, and Vaiśya males, ensuring his rights with responsibilities and signifying his advent into adulthood.
The tradition is widely discussed in ancient Samskṛta texts of Hinduism and varies regionally. The sacred thread or yajñopavīta (also referred to as Janeu, Jandhyam, Pūṇūl, Muñja and Janivara Yonya) has become one of the most important identifiers of the Upanayana ceremony in contemporary times, however this was not always the case. Typically, this ceremony should be performed before the advent of adulthood.