The theological concept known as panentheism—the idea that all of reality, the entire universe, is within God—has deep and far-reaching roots in the history of ideas. This volume is the first monograph to examine the history of panentheism in antiquity. For some ancient authors, the fundamental panentheistic intuition—that everything is in God—represents merely a speculative footnote in their philosophical thought. For others, however, it became the defining form of theological thought. The panentheistic mode of thought reached a high point in antiquity with Origen of Alexandria (185–253/54 CE), who, like no other author before him, developed a doctrine of the existence of the universe within God; for this reason, a more detailed study is devoted to him.