Using discursive institutionalism as an analytical framework, this article addresses how national actors build, coordinate and communicate discourses on EU defence policy (CSDP) at home. The empirical analysis is based on a comparative study of substantive and interactive discourses in France and Ireland, two contrasted cases. It demonstrates that France and Ireland frame and interpret elements of CSDP that best fit their needs, use them to promote their defence agenda in a legitimate and ‘European’ way and present CSDP as a natural continuation of their preferences. These defence agendas revolve around the preservation of France’s exceptionalism and Ireland’s neutrality. Discursive institutionalism, which methodologically sheds light on agents and institutional contexts, helps to understand the dynamics of constructive ambiguity, a discursive strategy often applied to CSDP and illustrated by these two cases.