Apollo or Apollon is one of the Olympian deities in classical Greek and Roman religion and Greek and Roman mythology. The national divinity of the Greeks, Apollo has been recognized as a god of archery, music and dance, truth and prophecy, healing and diseases, the Sun and light, poetry, and more. One of the most important and complex of the Greek gods, he is the son of Zeus and Leto, and the twin brother of Artemis, goddess of the hunt. Seen as the most beautiful god and the ideal of the kouros (ephebe, or a beardless, athletic youth). Apollo is known in Greek-influenced Etruscan mythology as Apulu.

As the patron deity of Delphi (Apollo Pythios), Apollo is an oracular god—the prophetic deity of the Delphic Oracle. Apollo is the god who affords help and wards off evil; various epithets call him the "averter of evil".

Medicine and healing are associated with Apollo, whether through the god himself or mediated through his son Asclepius. Apollo delivered people from epidemics, yet he is also a god who could bring ill-health and deadly plague with his arrows. The invention of archery itself is credited to Apollo and his sister Artemis. Apollo is usually described as carrying a silver or golden bow and a quiver of silver or golden arrows. Apollo's capacity to make youths grow is one of the best attested facets of his panhellenic cult persona. As a protector of the young (kourotrophos), Apollo is concerned with the health and education of children. He presided over their passage into adulthood. Long hair, which was the prerogative of boys, was cut at the coming of age (ephebeia) and dedicated to Apollo.

Apollo is an important pastoral deity, and was the patron of herdsmen and shepherds. Protection of herds, flocks and crops from diseases, pests and predators were his primary duties. On the other hand, Apollo also encouraged founding new towns and establishment of civil constitution. He is associated with dominion over colonists. He was the giver of laws, and his oracles were consulted before setting laws in a city.

As the god of mousike, Apollo presides over all music, songs, dance and poetry. He is the inventor of string-music, and the frequent companion of the Muses, functioning as their chorus leader in celebrations. The lyre is a common attribute of Apollo. In Hellenistic times, especially during the 5th century BCE, as Apollo Helios he became identified among Greeks with Helios, the personification of the Sun. In Latin texts, however, there was no conflation of Apollo with Sol among the classical Latin poets until 1st century CE. Apollo and Helios/Sol remained separate beings in literary and mythological texts until the 5th century CE.