This work examines early Christian self-definition and response to the world, according to the book of Acts. The author argues that early Christian self-definition and mission are intertwined. In other words, early Christian identity was at the same time the nascent faith's response to the world of paganism and Judaism. This book examines the historiography of Acts, the history of Redemption, the socio-ethnic and theological dimensions of earliest Christian self-definition, and the concepts of conversion, identity and mission. The work's specific contribution lies in its exploitation of Luke's distinctive use of the conversion of Saul of Tarsus, given its paradigmatic function in the Acts narrative, to "legitimize" a new Christian self for the early Christians, set in critical relation to the drama of their (Jewish) heritage. The author submits that this posture of the world is determined by Luke's understanding of the experience of God's new redemption in Jesus as the defining factor in the identity of Christians.