Lophophora williamsii or peyote () is a small, spineless cactus with psychoactive alkaloids, particularly mescaline. The English common name peyote is a Spanish loanword, which comes from the Nahuatl name peyōtl [ˈpejoːt͡ɬ], said to be derived from a root meaning "glisten" or "glistening". Other sources translate the Nahuatl word as "Divine Messenger". Native North Americans are likely to have used peyote, often for spiritual purposes, for at least 5,500 years.

Peyote is native to Mexico and southwestern Texas. It is found primarily in the Chihuahuan Desert and in the states of Coahuila, Nuevo León, Tamaulipas and San Luis Potosí among scrub, especially where there is limestone.

Known for its psychoactive properties when ingested, peyote is used worldwide as an entheogen and supplement to various transcendence practices, including meditation, psychonautics, and psychedelic psychotherapy. Peyote has a long history of ritualistic and medicinal use by indigenous Americans. It flowers from March through May, and sometimes as late as September. The flowers are pink, with thigmotactic anthers (like Opuntia).