During the first four centuries of the common era, scholars and theologians laid the ground work for Christian doctrines that have shaped the faith and practice of believers for two millenia. This was the formative period of Christianity when the major theological tenets of the faith were articulated. The writings of the earliest Christians continue to serve as a vital source of inspiration and guidance for Christians around the world. This Companion offers an overview of Christianity's foundational beliefs and practices. Providing an historiographical overview of the topic, it includes essays on the key thinkers and texts, as well as doctrines and practices that emerged during early Christian era. The volume covers the range of texts produced over four centuries and written by theologians hailing from throughout the Mediterranean world, including the Latin West, North Africa, and the Greek east. Written by an international team of scholars, this Companion serves an accessible introduction to the topic for students and scholars alike.