This paper investigates how entrepreneurialism has permeated into western military institutions and transformed their thinking, organizing and practice. It does so through an analytically structured history of how entrepreneurialist ideology has transformed the epistemological, ontological, and normative underpinnings of western militaries and in turn how this has affected their organizing and practice. The analysis will take hermeneutical approach and be based on a rich source material consisting of articles in military and defense journals, military doctrines, monographs from mainly US. Defense Colleges and policy and strategic documents. The covered period will be from the end of the Cold War until present day. The article finds that the influx of entrepreneurialism into western military institutions comes as a biproduct of broader discussions within these institutions about the (1) role of new (military) technologies, (2) the necessary skills and knowledge of military professionals and finally (3) the understanding of the military institution and its role and tasks within a complex and transforming (security) world.