This thesis examines whether the Islamic State of Iraq and Syria (ISIS) marks a new stage in the development of Salafi-jihadism. Based on a thorough examination of primary and secondary sources, this study concludes that the emergence of ISIS introduced three significant differences into the Salafi-jihadism world. First, sectarianism and the mass application of takfir to excommunicate Muslims have been at the core of ISIS's strategy. Second, ISIS's establishment of the proto-caliphate is a huge milestone in the history of Salafi-jihadism. Third, a propaganda campaign and the professional use of media are additional new characteristics that distinguish ISIS from the other Salafi-jihadist groups. The thesis concludes that ISIS marks a new stage in the development of Salafi-jihadism. Although ISIS has attempted to leave an extensive legacy, we believe that the establishment of the Islamic caliphate is the only lasting impact that ISIS will have on Salafi-jihadism ideology. Despite the terrible reputation ISIS has gained for its brutalities, the success that the group had in establishing a proto-caliphate-however briefly-will live forever, and may encourage future generations of Salafi-jihadists to undertake the same endeavor.