Military geographical research often requires direct engagement with military institutions. Although the morality of such engagements is often debated, the details of engagement in practice have been less scrutinised. Scrutiny is important, as military engagements can shape research-derived critiques and can influence the communication of research outcomes to both military and academic research communities. Military engagement comprises the communication of data, theories, and concepts about military activities and phenomena, with military personnel and institutions, in textual, representational, and interpersonal modes. The paper examines Geography's history of research engagement to show the complexities and debates around this seemingly straightforward idea. It then introduces a research project and wider research programme on the UK armed forces reserves which provides the empirical context from which we draw our observations about military engagement. We then consider two issues, language and institutional cultures, for their insights into the complexities of military engagement. We conclude by considering the politics of engagement in contemporary critical military geographical research.