Gnosticism is one of the significant religious and philosophical movements of the Late Antiquity. The present publication attempts to briefly describe the history of Gnosticism in the Antiquity, particularly the major gnostic systems of the second and third centuries. The textbook presents the most famous sources and also summarizes the history of modern research on Gnosticism. It deals with the foundations of the gnostic worldview, its conception of the origins and nature of the world, the creation of the humankind and the way the human beings had to go to reach salvation. It presents the most significant movements of Antique Gnosticism, Sethianism and Valentinianism, and also pays attention to Manichaeism and Mandaeism, which were influenced by gnostic ideas as well.