Theaetetus (Θεαίτητος) is a Greek name which could refer to:
- Theaetetus (mathematician) (c. 417 BC – 369 BC), a Greek geometer
- Theaetetus (dialogue), a dialogue by Plato, named after the geometer
- Theaetetus (crater), a lunar impact crater
- Theaetetus (poet) (Θεαίτητος ο σχολαστικός), a poet of Greek Anthology