The prolific Turkish author Harun Yahya attracted international attention after thousands of unsolicited copies of his large-format and lavishly illustrated book Atlas of Creation were sent free of charge from Istanbul, Turkey, to schools, universities and state leaders worldwide in 2007. This book stunt drew attention to Islamic creationism as a growing phenomenon, and to Harun Yahya as its most prominent proponent globally. Harun Yahya is allegedly the pen name of the Turkish author and preacher Adnan Oktar. Behind the brand name “Harun Yahya”, a highly prosperous religious enterprise is in operation, devoted not merely to the debunking of Darwinism, but also to the promotion of Islam. Backed by his supporters, Oktar channels vast financial resources into producing numerous books, dvds, websites and lately also television shows promoting his message. The aim of this dissertation is to shed light on the Harun Yahya enterprise by examining selected texts published in the framework of the enterprise. It describes, analyzes and contextualizes four key themes in the works of Harun Yahya, namely conspiracy theories, nationalism/neo-Ottomanism, creationism and apocalypticism/Mahdism. The dissertation traces the development of the enterprise from a religious community emerging in Turkey in the mid-1980s to a global da‘wa enterprise, and examines the way in which its discourse has changed over time. The dissertation’s point of departure is the notion that the Harun Yahya enterprise and the ideas it promotes must primarily be understood within the Turkish context from which it emerged. Drawing on analytical frameworks from social movement theory and rhetorical analysis as well as contemporary perspectives on Islamic da‘wa and activism, the study approaches Harun Yahya as a religious entrepreneur seeking market shares in the contemporary market for Islamic proselytism by adopting and adapting popular discourses both in the Turkish and global contexts. It examines how the Harun Yahya enterprise employs rhetorical and argumentative strategies in order to promote not merely a certain interpretation of Islam, but also increasingly Adnan Oktar and the Harun Yahya enterprise itself, by rhetorically placing its efforts into a cosmological framework.