This chapter will focus on a very rare topic in the academic literature: the secondary use of qualitative data collected by another researcher. The practice of secondary analysis has developed in political science and sociology over the last decade. Yet it raised specific issues in defence studies, as the formerly collected data can be put under the shade of secrecy or confidentiality. Thus is it possible to conduct a secondary analysis of qualitative data collected on defence questions (as interview data for instance)? Under what conditions can this be done? What are the limits encountered by the researcher when leading secondary analysis of qualitative data when it comes to defence topics? The chapter will first explain what is secondary analysis of qualitative data in defence studies, and what kind of methodological and ethical questions this method raises. It will secondly analyse the conditions needed in order to proceed to secondary analysis in defence studies. We will illustrate our argumentation with a case study regarding the secondary analysis of qualitative data collected on French-German military cooperation and defence policies and underline the potentiality and limits of this specific methods for defence studies, as Laurent Borzillo led a secondary analysis of qualitative data collected by Delphine Deschaux-Dutard on French and German defence policies in the frame of European defence policy since the end of the Cold War.