Passiflora, known also as the passion flowers or passion vines, is a genus of about 550 species of flowering plants, the type genus of the family Passifloraceae.

Passiflora species are widely cultivated for their striking flowers, flavorful fruits, traditional medicinal uses, and roles in dietary supplements and ayahuasca analogs, with several ornamental hybrids earning Royal Horticultural Society awards.

They are mostly tendril-bearing vines, with some being shrubs or trees. They can be woody or herbaceous.

Passion flowers produce regular and usually showy flowers with a distinctive corona. There can be as many as eight concentric coronal series, as in the case of P. xiikzodz. and Passiflora alata. The hallmark of the genus is the androgynophore, a central column to which the stamens and pistil are attached, which can be very long in some species such as Passiflora coactilis. The flower is pentamerous (except for a few Southeast Asian species) and ripens into an indehiscent fruit with numerous seeds.

The fruit ranges from 5–20 centimetres (2–8 in) long and 2.5–5 cm (1–2 in) across, depending upon the species or cultivar.

Many species of Passiflora have been found to contain beta-carboline harmala alkaloids, some of which are MAO inhibitors. The flower and fruit have only traces of these chemicals, but the leaves and the roots often contain more. The most common of these alkaloids is harman, but harmaline, harmalol, harmine, and harmol are also present. The species known to bear such alkaloids include: P. actinia, P. alata (winged-stem passion flower), P. alba, P. bryonioides (cupped passion flower), P. caerulea (blue passion flower), P. capsularis, P. decaisneana, P. edulis (passion fruit), P. eichleriana, P. foetida (stinking passion flower), P. incarnata (maypop), P. quadrangularis (giant granadilla), P. suberosa, P. subpeltata and P. warmingii.

Other compounds found in passion flowers are coumarins (e.g. scopoletin and umbelliferone), maltol, phytosterols (e.g. lutenin) and cyanogenic glycosides (e.g. gynocardin) which render some species, i.e. P. adenopoda, somewhat poisonous. Many flavonoids and their glycosides have been found in Passiflora, including apigenin, benzoflavone, homoorientin, 7-isoorientin, isoshaftoside, isovitexin (or saponaretin), kaempferol, lucenin, luteolin, n-orientin, passiflorine (named after the genus), quercetin, rutin, saponarin, shaftoside, vicenin and vitexin. Maypop, blue passion flower (P. caerulea), and perhaps others contain the flavone chrysin. Also documented to occur at least in some Passiflora in quantity are the hydrocarbon nonacosane and the anthocyanidin pelargonidin-3-diglycoside.

The genus is rich in organic acids including formic, butyric, linoleic, linolenic, malic, myristic, oleic and palmitic acids as well as phenolic compounds, and the amino acid α-alanine. Esters like ethyl butyrate, ethyl caproate, n-hexyl butyrate and n-hexyl caproate give the fruits their flavor and appetizing smell. Sugars, contained mainly in the fruit, are most significantly d-fructose, d-glucose and raffinose. Among enzymes, Passiflora was found to be rich in catalase, pectin methylesterase and phenolase.