This dissertation explores the sources that the author of the Apocalypse used to create his description of the heavenly liturgy. Many previous treatments of this subject have overstated the conclusions that can be drawn from our evidence for Christian liturgical practice in the late-first century CE. In order to determine which of the elements found in Rev 4-5 might have been taken from an early Christian service of worship, the available liturgical evidence is examined to ascertain what we can say that we know about Christian worship at the end of the first century CE, and to correct some mistaken conclusions that have appeared in earlier scholarship. This examination includes the first-century evidence for the use of the Sanctus, hymns, doxologies, the use of incense, the amen, and the alleluia. The results of this survey are disappointing, as the pieces that we need to be able to reconstruct the ways in which Christians worshipped in the first century are largely lacking, and many of these prayers and practices remain beyond our reach. Turning to the texts of Rev 4-5 themselves, the dissertation tries to identify the sources of the author's imagery for his picture of what the heavenly worship of God looked like, focusing on what may have been derived from a service of Christian worship. Contemporary Jewish and Christian liturgical practices were likely to have been one source of this imagery, along with the OT and Jewish apocalyptic literature, elements of ancient Near Eastern throne room scenes, Roman imperial court ceremonial, and his own imagination. Another concern of the dissertation asks whether the Apocalypse was read at a liturgy, focusing on the introductory and concluding passages of the text (Rev 1:4-8 and 22:6-21), which some have argued take the form of a liturgical dialogue between the lector and assembly. This theory helps to explain some parts of these passages better then others, but most problematic is the fact that our evidence for worship practices in the first centuries remains incomplete, and we cannot be sure that liturgical dialogues were a part of Christian liturgy at this early date.