四帝共治制（英语：Tetrarchy）是罗马皇帝戴克里先创立的一个治理模式。由于他看出罗马帝国过去两、三百年间世袭制度的缺点，整个国家积弱不振，甚至引发空前绝后的三世纪危机。于是他大规模地将全国的政治体制整个翻转，即废除了帝位世袭及君王独裁的制度，创新一个四帝共治制的治理模式：两位最高级的领导人（或称皇帝）任职为奥古斯都及两位次级领导人（或称副皇帝）任职为凯撒，即全境共有四位领导人去分治东、西罗马帝国。而奥古斯都的任期是有期限的，届满后得自动退位由统帅继任之。

The term "tetrarchy" (from the Greek τετραρχία "leadership of four [people]") describes any form of government where power is divided among four individuals, but in modern usage usually refers to the system instituted by Roman Emperor Diocletian in 293, marking the end of the Crisis of the Third Century and the recovery of the Roman Empire. This Tetrarchy lasted until c. 313, when internecine conflict eliminated most of the claimants to power, leaving Constantine in the East and Licinius in the West.