Xenocrates of Chalcedon was a Greek philosopher of the 4th century BCE, living from approximately 396 to 314 BCE. He moved to Athens as a young man and became a student of Plato. After Plato’s death, he studied under Speusippus, and in 339 BCE he was elected the third head, or scholarch, of Plato’s Academy, a position he held for 25 years. Ancient sources describe him as a man of austere and unwavering moral character.

He was a prolific writer, but none of his works survive complete. They are known only through titles and fragments quoted by later authors. His many lost treatises covered a wide range of topics, including On the Good, On the Soul, On the Gods, and On Happiness, aiming to systematize Platonic doctrine.

As a pivotal early Platonist, Xenocrates played a crucial role in shaping the school's teachings. According to modern scholars, his most lasting contribution was his formal division of philosophy into three parts: Physics (the study of nature), Ethics, and Logic, a framework that became standard in later philosophy. He also developed influential interpretations of Plato's ideas, identifying the Platonic Forms with mathematical numbers and proposing a system of intermediate divine beings, or daemons. His long leadership helped stabilize and define the Academy after Plato's death, influencing later Platonist and Stoic thought.