Theano (Greek: Θεανώ; 6th-century BC) was a Pythagorean philosopher. She was said by many to have been the wife of Pythagoras, although others made her the wife of Brontinus. A few fragments and letters ascribed to her have survived which are of uncertain authorship. She is believed by some historians to have been a student of Pythagoras and later a teacher in the Pythagorean school, which had 28 female Pythagoreans participating in it .
Little is known about the life of Theano, and the ancient sources are confused. According to one tradition, she came from Crete and was the daughter of Pythonax, but others said she came from Croton and was the daughter of Brontinus. She was said by many to have been the wife of Pythagoras, although another tradition made her the wife of Brontinus. Iamblichus refers to Deino as the wife of Brontinus.
The children ascribed to Pythagoras and Theano included three daughters, Damo, Myia, and Arignote, and a son, Telauges.
The writings attributed to Theano were: Pythagorean Apophthegms, Female Advice, On Virtue, On Piety, On Pythagoras, Philosophical Commentaries, and Letters. None of these writing have survived except a few fragments and letters of uncertain authorship. Attempts have been made to assign some of these fragments and letters to the original Theano (Theano I) and some to a later Theano (Theano II), but it is likely that they are all pseudonymous fictions of later writers, which attempt to apply Pythagorean philosophy to a woman's life. The surviving fragment of On Piety concerns a Pythagorean analogy between numbers and objects; the various surviving letters deal with domestic concerns: how a woman should bring up children, how she should treat servants, and how she should behave virtuously towards her husband.
Mary Ritter Beard claimed that her treatise On Virtue contained the doctrine of the golden mean.
A celebrated female philosopher of the Pythagorean School, appears to have been the wife of Pythagoras, and the mother by him of Telauges, Mnesarchus, Myia , and Arignoté; but the accounts respecting her were various (Diog. Laert. viii. 42; Suidas, s. h. v.). Letters ascribed to her, but not genuine, exist, and are edited by Hercher (1873).