Antisthenes of Athens was a Greek philosopher who lived from approximately 445 to 365 BCE. He was a devoted pupil of Socrates and is considered a foundational figure for the Cynic school of philosophy. His mother was Thracian, which meant he did not have full Athenian citizenship. He was known for an ascetic lifestyle and taught that virtue was the only requirement for happiness. After Socrates' death, he taught at the Cynosarges gymnasium in Athens. According to ancient accounts, his pupils included Diogenes of Sinope, who became the most famous Cynic.

His philosophy focused on ethics, advocating for self-sufficiency, hard work, and the rejection of conventional desires like wealth and pleasure. He believed virtue could be taught and, once gained, could not be lost. Scholars note he was critical of abstract philosophical theories, favoring practical moral instruction. He was a prolific writer, but none of his works survive intact. Ancient sources credit him with over 60 titles, including Socratic dialogues and interpretations of Homer, though all are now lost. The exact connection between his teachings and the later Cynic movement is a subject of modern scholarly debate.

Antisthenes is historically important as a direct link between Socrates and later philosophical traditions. His ideas on virtue and asceticism laid the groundwork for Cynicism and subsequently influenced Zeno of Citium, the founder of Stoicism. He represents a significant strand of early Socratic thought that existed alongside the works of Plato and Xenophon.