By the advent of Christianity mysticism has started practicing in the Christian religious life and has been influenced by external and internal sources during its development and formation. This essay tries to survey the formative period of the Christian mysticism, and includes two parts: In the first part the influence of following factors on Christian mysticism have been dealt with: Jewish heritage-that is, the historical and environmental relations of Jewish and Christian communities and their similarities in the religious beliefs and rituals-Hebrew Bible and Philo's treatises, religious texts-such as Didache and Apocalyptic and apocryphal literature-mysterious religions, and Gnostics and Hermetic rituals. Moreover, the impact of Platonic and Neo-Platonic schools on Christians' tendency towards mysticism has been mentioned. In the second part, the influence of internal sources such as Gospels, the mystical teachings of Christ, Paul and John, have been studied. Finally, we come to the conclusion that Christian mysticism, in spite of external influences, has mostly been impacted by the Gospels and mystical and moral teachings of Christ and his ascetic life.