Antiphon the Sophist was an Athenian intellectual active in the late 5th century BCE, during the Classical period. He was part of the Sophist movement, teachers who offered instruction in rhetoric and virtue. His identity is a subject of scholarly debate. He has traditionally been conflated with another Athenian named Antiphon, who was a speechwriter and politician. Many modern scholars now distinguish them as separate individuals based on differences in their writings and ancient testimonies, though some sources maintain they could be the same person.

His surviving works are fragmentary, known from papyrus discoveries and quotations by later authors. They include philosophical treatises such as On Truth, which argues for a distinction between human laws and natural justice, and On Concord, which advocates for social harmony. Other attributed works are the Politicus (a political treatise) and a work on the Interpretation of Dreams. A set of model courtroom speeches called the Tetralogies is also associated with the name Antiphon; these are often linked to the speechwriter, but their educational nature connects them to Sophistic teaching.

Antiphon the Sophist is significant for his early contributions to moral and political thought. His arguments in On Truth provide a radical exploration of the conflict between societal convention and natural advantage, a key theme in Sophistic philosophy that later thinkers like Plato engaged with. The Tetralogies, regardless of their exact authorship, are historically important as the earliest surviving examples of full Athenian judicial oratory and were likely used to teach rhetorical technique. The ongoing debate about his identity makes him a central figure for understanding the links between abstract philosophy, professional rhetoric, and politics in ancient Athens.