The study takes up the topic of the evolution of Hamas' military action from the foundation of the Izz al-Din al-Qassam Brigades between 1987 and 1992, the movement's military wing, and beyond, drawing upon memoirs and testimonies of the movement's political and military leaders in Palestine and on available data regarding military confrontations with the Israeli occupation. The study starts from the assumption that the evolution of Hamas's military action as an active "agent" in the region differs across the different stages of the Palestinian-Israeli conflict on the one hand, and with the development of the movement's political thought and relations with regional and international systems on the other. These stages have been formational of the movement's variable identity, one that has led it to defining its regional interest and role on the basis of military strength. It transformed into a "semi-classical" army in Gaza specifically, after having been a movement of modestly equipped and armed groupings, as it continues to be to this day in the West Bank. This study attempts to monitor this evolution across the successive confrontations with the Israeli occupation in the wars of 2008, 2012 and 2014.