The present article discusses why the study of Christian Apocrypha and Parabiblical Traditions is crucial not only for the understanding of early Christian History but also for the theological field of New Testament Exegesis. It starts with the author’s definition of Christian Apocrypha and Parabiblica and offers examples for the heuristic value of such an understanding. It discusses the impact of apocryphal writings and parabiblical traditions for the reception history of the New Testament and for the understanding of the history, understanding and development of genres of ancient Christian writings like apocalypses and Gospels. After this it develops and discusses three major theses about the impact of Christian Apocrypha for the understanding of the New Testament canon, its fundamental openness and history even after its formal closure. Finally, it offers opportunities of inter-theological interdisciplinary dialogue.