Theaetetus (Θεαίτητος) is a Greek name which may refer to:

• Theaetetus (mathematician) (c. 417 BC – 369 BC), Greek geometer
• Theaetetus (dialogue), a dialogue by Plato, named after the geometer
• Theaetetus (crater), a lunar impact crater
• Theaetetus (poet) (fl. 3rd century BC), Greek poet
• Theaetetus of Cyrene (Θεαίτητος ὁ Κυρηναῖος) (fl. 270 BC), Greek poet
• Theaetetus Scholasticus (Θεαίτητος ὁ σχολαστικός) (fl. 6th century AD), Greek poet