Papilio machaon, the Old World swallowtail, is a butterfly of the family Papilionidae. The butterfly is also known as the common yellow swallowtail or simply the swallowtail. It is the type species of the genus Papilio. This widespread species is found in much of the Palearctic and in North America.

Swallowtail butterflies are large, colorful butterflies in the family Papilionidae, and include over 550 species. Though the majority are tropical, members of the family inhabit every continent except Antarctica. The family includes the largest butterflies in the world, the birdwing butterflies of the genus Ornithoptera.