This chapter discusses the challenge of knowing about what is purposefully rendered difficult to know about matters of defense, intelligence and security. In the light of this challenge, the chapter seeks to develop an appreciation of how commentators across varied disciplines characterize the relation between knowledge and ignorance in matters associated with intelligence, security and national secrecy. It explores how ignorance can become a resource when dealing with defense and security matters. The chapter explores how ignorance and collective identity relate to each other before, during and after acts of violence. It considers methodological issues arising from the study of security and ignorance that have implications for the wider community of ignorance researchers. It is through the study of the spatial and temporal management of the contradictions of ‘secret keeping’ that it is possible to develop a sense of how tightly twined and mutually constitutive knowledge and ignorance can be in practice as well as how contradiction underpins state secrecy.