Speusippus (c. 408 – 339/8 BCE) is an ancient Greek philosopher.

Speusippus is Plato's nephew by his sister Potone.

After Plato's death, Speusippus inherits the Academy and remains its head for the next eight years.

However, following a stroke, he passes the chair to Xenocrates.

Although the successor to Plato in the Academy, he frequently diverges from Plato's teachings.

He rejects Plato's Theory of Forms, and whereas Plato had identified the Good with the ultimate principle, Speusippus maintainsthat the Good is merely secondary.

He also argues that it is impossible to have satisfactory knowledge of any thing without knowing all the differences by which it is separated from everything else.