Rebirth in Buddhism refers to the teaching that the actions of a sentient being lead to a new existence after death, in an endless cycle called saṃsāra. This cycle is considered to be dukkha, unsatisfactory and painful. The cycle stops only if Nirvana (liberation) is achieved by insight and the extinguishing of craving. Rebirth is one of the foundational doctrines of Buddhism, along with karma and Nirvana. Rebirth was a key teaching of early Buddhism along with the doctrine of karma (which it shared with early Indian religions like Jainism). In Early Buddhist Sources, the Buddha claims to have knowledge of his many past lives. Rebirth and other concepts of the afterlife have been interpreted in different ways by different Buddhist traditions.

The rebirth doctrine, sometimes referred to as reincarnation or transmigration, asserts that rebirth takes place in one of the six realms of samsara, the realms of gods, demi-gods, humans, the animal realm, the ghost realm and hell realms. Rebirth, as stated by various Buddhist traditions, is determined by karma, with good realms favored by kusala karma (good or skillful karma), while a rebirth in evil realms is a consequence of akusala karma (bad or unskillful karma). While nirvana is the ultimate goal of Buddhist teaching, much of traditional Buddhist practice has been centered on gaining merit and merit transfer, whereby one gains rebirth in the good realms and avoids rebirth in the evil realms.

The rebirth doctrine has been a subject of scholarly studies within Buddhism since ancient times, particularly in reconciling the rebirth doctrine with its anti-essentialist anatman (not-self) doctrine. The various Buddhist traditions throughout history have disagreed on what it is in a person that is reborn, as well as how quickly the rebirth occurs after each death.

Some Buddhist traditions assert that vijñana (consciousness), though constantly changing, exists as a continuum or stream (santana) and is what undergoes rebirth. Some traditions like Theravada assert that rebirth occurs immediately and that no "thing" (not even consciousness) moves across lives to be reborn (though there is a causal link, like when a seal is imprinted on wax). Other Buddhist traditions such as Tibetan Buddhism posit an interim existence (bardo) between death and rebirth, which may last as long as 49 days. This belief drives Tibetan funerary rituals. A now defunct Buddhist tradition called Pudgalavada asserted there was an inexpressible personal entity (pudgala) which migrates from one life to another.

There is no word corresponding exactly to the English terms "rebirth", "metempsychosis", "transmigration" or "reincarnation" in the traditional Buddhist languages of Pāli and Sanskrit. Rebirth is referred to by various terms, representing an essential step in the endless cycle of samsara, terms such as "re-becoming" or "becoming again" (Sanskrit: punarbhava, Pali: punabbhava), re-born (punarjanman), re-death (punarmrityu), or sometimes just "becoming" (Pali/Sanskrit: bhava), while the state one is born into, the individual process of being born or coming into the world in any way, is referred to simply as "birth" (Pali/Sanskrit: jāti). The entire universal process of beings being reborn again and again is called "wandering about" (Pali/Sanskrit: saṃsāra).

Some English-speaking Buddhists prefer the term "rebirth" or "re-becoming" (Sanskrit: punarbhava; Pali: punabbhava) to "reincarnation" as they take the latter to imply an entity (soul) that is reborn. Buddhism denies there is any such soul or self in a living being, but does assert that there is a cycle of transmigration consisting of rebirth and redeath as the fundamental nature of existence.

Before the time of the Buddha, many ideas on the nature of existence, birth and death were in vogue. The early layers of the Vedas do not mention the doctrine of Karma and rebirth but mention the belief in an afterlife. According to Sayers, these earliest layers of the Vedic literature show ancestor worship and rites such as sraddha (offering food to the ancestors). The later Vedic texts such as the Aranyakas and the Upanisads show a different soteriology based on reincarnation, they show little concern with ancestor rites, and they begin to philosophically interpret the earlier rituals. The idea of reincarnation and karma have roots in the Upanishads of the late Vedic period, predating the Buddha and the Mahavira. The Sramana schools affirmed the idea of soul, karma and cycle of rebirth. The competing Indian materialist schools denied the idea of soul, karma and rebirth, asserting instead that there is just one life, there is no rebirth, and death marks complete annihilation. From these diverse views, Buddha accepted the premises and concepts related to rebirth, but introduced innovations. According to various Buddhist scriptures, Buddha believed in other worlds,

Since there actually is another world (any world other than the present human one, i.e. different rebirth realms), one who holds the view 'there is no other world' has wrong view...