Global jihadi terrorism remains a threat to Western societies nearly fifteen years after the 9/11 attacks. Despite the sustained and costly War on Terror, the phenomenon of global jihadi terrorism is, and will likely remain a threat for decades to come. What do we know about the causes of this form of terrorism, and upon what empirical basis is this knowledge based? This thesis offers a review of the post-9/11 scholarly literature on the causes of global jihadi terrorism. The review is particularly aimed at assessing explanations at the individual- and group-level. Furthermore, the review examines whether the empirical basis and methodological procedures employed in the studies in question support the conclusions and explanations offered by their authors. While select studies present robust findings and explanations, a large swath of the scholarship lacks a solid empirical basis, and offers little transparency and rigor. Despite the dearth of high quality data and methodological stringency, many authors fail to properly communicate the limitations, shortcomings and contingencies of their conclusions. Therefore, there is an urgent need for robust, reliable and methodologically sound empirical studies that can provide a more solid foundation for valid explanations, generalizations and contingent theory-building.