Much scholarship has recently been done on the Satanology (Satan-concept) of New Testament books or writers. This study attends to the Satanology of early non-canonical Christian writings, which have been comparatively under-researched. The literature examined includes the Apostolic Fathers and other texts that can be reliably dated to c. 100–150 c.e., namely Ascension of Isaiah, Apocalypse of Peter, Odes of Solomon, Gospel of Truth, Ptolemy’s Letter to Flora, and Justin Martyr’s writings. Over 160 certain or probable references to Satan, under various designations, are identified. Analysis of this data set proceeds in two directions. The first looks at the concept’s explanatory power: for what kinds of evil did Satanology help to account? The discussion traverses various loci of perceived satanic activity, from the human heart to community boundaries to earthly political authorities to a dualistic cosmos to the abstract realm of ideas. The second analytical section explores ways that Christian writers and communities incorporated Satanology into their religious life through liturgical forms, hermeneutics for reading the Jewish Scriptures, and theological debates about the nature of God and evil. Satanology is found to have been a pervasive and distinctive feature of Christianity in the early subapostolic period.