This volume includes English translations of several documents written by the Luciferians, a group of fourth-century Christians whose name derives from the bishop Lucifer of Cagliari, that highlight connections between developments in Christian theology and local Christian communities in the course of the fourth century. The most important document, the Luciferian petition called the Libellus precum, has never been published in English. The theological tract De Trinitate was last published in English in an otherwise unknown anonymous version from 1721. An introduction provides an overview of the development of late antique theology and Christianity, a discussion of Luciferian beliefs, and discussions of the texts.