Pytheas of Massalia was a Greek geographer, explorer and astronomer from the Greek colony of Massalia. He made a voyage of exploration to northwestern Europe in about 325 BC, but his account of it, known widely in antiquity, has not survived and is now known only through the writings of others.

Massalia was an ancient Greek colony (apoikia) on the Mediterranean coast, east of the Rhône. Settled by the Ionians from Phocaea in 600 BC, this apoikia grew up rapidly, and its population set up many outposts for trading in modern-day Spain, Corsica and Liguria. Massalia persisted as an independent colony until the Roman campaign in Gaul in the 1st Century BC. The ruins of Massalia still exist in the contemporary city of Marseille, which is considered the oldest city of France and one of Europe's oldest continuously inhabited settlements.