Banisteriopsis caapi, also known as, caapi, soul vine, yagé (yage), or ayahuasca (the latter of which also refers to the psychedelic decoction made with the vine and a plant source of dimethyltryptamine) is a South American liana of the family Malpighiaceae. It is commonly used as an ingredient of ayahuasca, a decoction with a long history of its entheogenic use and holds status as a "plant teacher" among the Indigenous peoples of the Amazon rainforest.

It was used by Indigenous peoples of South America for centuries, but it was first documented by Europeans in the 16th century and formally identified by botanist Richard Spruce in 1851. According to The CRC World Dictionary of Plant Names by Umberto Quattrocchi, the naming of the genus Banisteriopsis was dedicated to John Banister, a 17th-century English clergyman and naturalist. An earlier name for the genus was Banisteria and the plant is sometimes referred to as Banisteria caapi. Other names include Banisteria quitensis, Banisteriopsis inebrians, and Banisteriopsis quitensis.

It is a giant vine that can grow up to 30 meters long, with pale flowers that bloom infrequently and resembles related species like Banisteriopsis membranifolia and B. muricata. It contains beta-carboline alkaloids and polyphenols.

Its legal status varies by country: it is largely unregulated in the United States (with specific religious exemptions for use of the ayahuasca decoction), ambiguously legal in Canada and parts of Australia, and effectively illegal in France despite past religious use rulings.

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