毕达哥拉斯（希腊语：Πυθαγόρας，约前580年－前500年），古希腊哲学家、数学家和音乐理论家。

毕达哥拉斯的哲学思想受到俄耳甫斯的影响，具有一些神秘主义因素。从他开始，希腊哲学开始产生了数学的传统。毕氏曾用数学研究乐律，而由此所产生的“和谐”的概念也对以后古希腊的哲学家有重大影响。毕达哥拉斯还是传统上所知的勾股定理（又称毕达哥拉斯定理）首先发现者（有学派说是巴比伦人先发现,亦有说是中国人发现）。

在宇宙论方面，毕达哥拉斯结合了米利都学派以及自己有关数的理论。他认为存在着许多但有限个世界，并坚持大地是圆形的，不过则抛弃了米利都学派的地心说。

Pythagoras of Samos (US /pɪˈθæɡərəs/; UK /paɪˈθæɡərəs/; Greek: Πυθαγόρας ὁ Σάμιος Pythagóras ho Sámios "Pythagoras the Samian", or simply Πυθαγόρας; Πυθαγόρης in Ionian Greek; c. 570 – c. 495 BC) was an Ionian Greek philosopher, mathematician, and has been credited as the founder of the movement called Pythagoreanism. Most of the information about Pythagoras was written down centuries after he lived, so very little reliable information is known about him. He was born on the island of Samos, and traveled, visiting Egypt and Greece, and maybe India, and in 520 BC returned to Samos. Around 530 BC, he moved to Croton, in Magna Graecia, and there established some kind of school or guild.