This chapter is based on our dissertation dealing with the genesis, practices and uses of the European Security and Defence Policy with a focus on the comparison between France and Germany both in the genesis and daily practices and representations of ESDP actors (military and diplomats). More precisely, we lead over 130 qualitative interviews with high military officials, diplomats and political leaders in Paris, Berlin, Bonn and Brussels. Here we focus on what it means to study the military with a qualitative and comparative methodology. We will therefore raise three main issues, which are intertwined in our research. The first issue will be the qualitative perspective and the questions it raises regarding the specificity of the military mission, with is often confidential. The second issue is to raise concretely the question of the implementation of the qualitative method in the military field in a comparative perspective : how to ask questions, so as theses questions make sense to the interviewees ? The last issue will address the question of reflexivity, and more precisely of the position of the enquirer before the military officers. What does it mean, and how does it impact the research ? We will of course rely on our case study (French and German officers in CSDP) to draw empirical examples, so as to illustrate the three issues raised in this chapter.