Mahayana is a major branch of Buddhism, along with Theravada. It is a broad group of Buddhist traditions, texts, philosophies, and practices developed in ancient India (c. 1st century BCE onwards). Mahāyāna accepts the main scriptures and teachings of early Buddhism but also recognizes various doctrines and texts that are not accepted by Theravada Buddhism as original. These include the Mahāyāna sūtras and their emphasis on the bodhisattva path and Prajñāpāramitā. Vajrayana or Mantra traditions are a subset of Mahāyāna which makes use of numerous Tantric methods Vajrayānists consider to help achieve Buddhahood.

Mahāyāna also refers to the path of the bodhisattva striving to become a fully awakened Buddha for the benefit of all sentient beings, and is thus also called the "Bodhisattva Vehicle" (Bodhisattvayāna). Mahāyāna Buddhism generally sees the goal of becoming a Buddha through the bodhisattva path as being available to all and sees the state of the arhat as incomplete. Mahāyāna also includes numerous Buddhas and bodhisattvas that are not found in Theravada (such as Amitābha and Vairocana). Mahāyāna Buddhist philosophy also promotes unique theories, such as the Madhyamaka theory of emptiness (śūnyatā), the Vijñānavāda ("the doctrine of consciousness" also called "mind-only"), and the Buddha-nature teaching.

While initially a small movement in India, Mahāyāna eventually grew to become an influential force in Indian Buddhism. Large scholastic centers associated with Mahāyāna such as Nalanda and Vikramashila thrived between the 7th and 12th centuries. In the course of its history, Mahāyāna Buddhism spread from South Asia to East Asia, Southeast Asia and the Himalayan regions. Various Mahāyāna traditions are the predominant forms of Buddhism found in China, Korea, Japan, Taiwan, Singapore, Vietnam, Philippines, Malaysia and Indonesia. Since Vajrayana is a tantric form of Mahāyāna, Mahāyāna Buddhism is also dominant in Tibet, Mongolia, Bhutan, and other Himalayan regions. It has also been traditionally present elsewhere in Asia as a minority among Buddhist communities in Nepal, Malaysia, Indonesia and regions with Asian diaspora communities.

As of 2010, the Mahāyāna tradition was the largest major tradition of Buddhism, with 53% of Buddhists belonging to East Asian Mahāyāna and 6% to Vajrayana, compared to 36% to Theravada.

According to Jan Nattier, the term Mahāyāna ("Great Vehicle") was originally an honorary synonym for Bodhisattvayāna ("Bodhisattva Vehicle"), the vehicle of a bodhisattva seeking buddhahood for the benefit of all sentient beings. The term Mahāyāna (which had earlier been used simply as an epithet for Buddhism itself) was therefore adopted at an early date as a synonym for the path and the teachings of the bodhisattvas. Since it was simply an honorary term for Bodhisattvayāna, the adoption of the term Mahāyāna and its application to Bodhisattvayāna did not represent a significant turning point in the development of a Mahāyāna tradition.

The earliest Mahāyāna texts, such as the Lotus Sūtra, often use the term Mahāyāna as a synonym for Bodhisattvayāna, but the term Hīnayāna is comparatively rare in the earliest sources. The presumed dichotomy between Mahāyāna and Hīnayāna can be deceptive, as the two terms were not actually formed in relation to one another in the same era.

Among the earliest and most important references to Mahāyāna are those that occur in the Lotus Sūtra (Skt. Saddharma Puṇḍarīka Sūtra) dating between the 1st century BCE and the 1st century CE. Seishi Karashima has suggested that the term first used in an earlier Gandhāri Prakrit version of the Lotus Sūtra was not the term mahāyāna but the Prakrit word mahājāna in the sense of mahājñāna (great knowing). At a later stage when the early Prakrit word was converted into Sanskrit, this mahājāna, being phonetically ambivalent, may have been converted into mahāyāna, possibly because of what may have been a double meaning in the famous Parable of the Burning House, which talks of three vehicles or carts (Skt: yāna).

In Chinese, Mahāyāna is called 大乘 (dàshèng, or dàchéng), which is a calque of maha (great 大) yana (vehicle 乘). There is also the transliteration 摩诃衍那. The term appeared in some of the earliest Mahāyāna texts, including Emperor Ling of Han's translation of the Lotus Sutra. It also appears in the Chinese Āgamas, though scholars like Yin Shun argue that this is a later addition. Some Chinese scholars also argue that the meaning of the term in these earlier texts is different from later ideas of Mahāyāna Buddhism.