Amitābha (Sanskrit pronunciation: [ɐmɪˈtaːbʱɐ], "Measureless" or "Limitless" Light), also known as Amituofo in Chinese, Amida in Japanese, Amita-bul in Korean, and Öpakmé in Tibetan, is one of the main Buddhas of Mahayana Buddhism and the most widely venerated Buddhist figure in East Asian Buddhism. Amitābha is also known by the name Amitāyus ("Measureless Life").

Amitābha is the main figure in two influential Indian Buddhist Mahayana Scriptures: the Sutra of Measureless Life and the Amitābha Sūtra. According to the Sutra of Measureless Life, Amitābha established a pure land of perfect peace and happiness, called Sukhāvatī ("Blissful"), where beings who mindfully remember him with faith may be reborn and then quickly attain enlightenment. The pure land is the result of a set of vows Amitābha made long ago. As his name means Limitless Light, Amitābha's light is said to radiate throughout the cosmos and shine on all beings. Because of this, Amitābha is often depicted radiating light, a symbol for his wisdom. As per the name Amitāyus, this Buddha is also associated with infinite life, since his lifespan is said to be immeasurable. Amitābha's measureless life is seen as being related to his infinite compassion.

Amitābha devotion is particularly prominent in East Asian Buddhism, where the practice of mindfulness of Amitābha Buddha (known as nianfo in Chinese, nembutsu in Japanese) is seen as a path to liberation open to everyone. Amitābha is also the principal Buddha in Pure Land Buddhism, which is a tradition focused on attaining birth in the pure land by relying on the power of Amitābha (also known as "Other Power") and faithfully reciting Amitabha's name. Amitābha is also a major deity in Tibetan Buddhism. where he is associated with pure land practices, as well as phowa (the transference of consciousness at the time of death).

The names Amitāyus and Amitābha (in various Chinese transliterations and translations) are used interchangeably in East Asian Buddhism. In Tibetan Buddhism however, Amitāyus is distinguished from Amitābha, and they are depicted differently in Himalayan art. Amitāyus is also known as a Buddha of long life in Tibetan Buddhism. In East Asian Buddhism, Amitābha is most often depicted as part of a triad with the two bodhisattvas Avalokiteśvara and Mahāsthāmaprāpta. In Tibetan Buddhism, the triad includes Avalokiteśvara and Vajrapani (or Padmasambhava) instead.

The most influential Amitābha focused Mahayana sutras are two sutras known by the Sanskrit title Sukhāvatī-vyūha (Blissful Array, or the Array of Sukhāvatī). These two are the Short Sukhāvatīvyūha Sūtra (also known as the Amitābha Sutra) and the Larger Sukhāvatīvyūha Sūtra (also known as the Sutra of Infinite Life). These sutras are the main Indian Mahayana sources for the teachings on Amitābha and his pure land. In these sutras, Amitābha is a transcendent and immortal Buddha who resides in a pure buddhafield that he created. This pure land is located billions of worlds away in the western direction and all beings can attain rebirth there, where they can swiftly become Buddhas themselves.

According to the Sūtra of Limitless Life, eons ago, Amitābha was a bodhisattva monk named Dharmākara. In some versions of the sūtra, Dharmākara is described as a former king who, having come into contact with Buddhist teachings through the buddha Lokeśvararāja, renounced his throne and became a monk. For five eons (kalpas), Dharmākara contemplated all the qualities of all the pure buddhafields (realms created by a Buddha existing outside of ordinary reality) throughout the cosmos. He then resolved to become a Buddha and to create the best of all pure buddha-fields possessed of many supreme qualities.

The sutra then recounts how Dharmākara made a series of bodhisattva vows (praṇidhāna), pledging that unless these vows were fulfilled, he would not attain Buddhahood. Different versions of the text list varying numbers of these vows (the most common sutra contains forty eight vows), which serves as the foundation for Pure Land doctrine. These solemn resolutions set out the type of pure land Dharmākara aspired to create, the conditions under which beings might be born into that world, and what kind of beings they would be. After many eons of bodhisattva practice, Dharmākara became Amitābha Buddha (his enlightenment having occurred ten kalpas ago). Since he now presides over the Pure Land of Sukhāvatī ("Utmost Bliss") in the western direction, it is understood that his vows were indeed fulfilled.

Among these "past vows", Dharmākara ensured that all beings born in his land would never fall into lower realms, and would possess golden divine bodies with many superpowers. He also vowed that they would be firmly established on the path to Buddhahood and could enjoy profound peace, happiness and an unlimited lifespan there. Amitābha’s name would be glorified by countless Buddhas, and those who sincerely place their trust in him and wish to be reborn in his Pure Land can attain birth there.