Papilio is a genus in the swallowtail butterfly family, Papilionidae, as well as the only representative of the tribe Papilionini. The word papilio is Latin for butterfly. It includes the common yellow swallowtail (Papilio machaon), which is widespread in the Northern Hemisphere and the type species of the genus, as well as a number of other well-known North American species such as the western tiger swallowtail (Papilio rutulus). Familiar species elsewhere in the world include the Mormons (Papilio polytes, Papilio polymnestor, Papilio memnon, and Papilio deiphobus) in Asia, the orchard and Ulysses swallowtails in Australia (Papilio aegeus, Papilio ulysses, respectively) and the citrus swallowtail of Africa (Papilio demodocus). Older classifications of the swallowtails tended to use many rather small genera. More recent classifications have been more conservative, and as a result a number of former genera are now absorbed within Papilio, such as Achillides, Eleppone, Druryia, Heraclides (giant swallowtails), Menelaides, Princeps, Pterourus (tiger swallowtails), and Sinoprinceps. The genus as recognized by modern systems has about 200 members. The genus Chilasa is regarded as a subgenus of Papilio by some workers, as are the baggy-tailed swallowtails (Agehana), although the latter taxon is usually considered a subgenus of Chilasa. Many of the larvae resemble bird droppings during a development stage. Adults are edible to birds and some species are mimics.

In their larval form, members of Papilio typically feed upon plants of Rutaceae including common ornamental and agriculturally important species such as Citrus species, Murraya species, Choisya species and Calodendrum species. Caterpillars sequester terpenoids from their diet to produce a foul smelling oil used in defence.