How should international law deal with the uncertainty arising from the rise of irregular forms of warfare? In the past decade, this question has been the topic of several reports produced by international groups of experts in the field of conflict and security law. The most recent examples include the study on the notion of the ‘direct participation in hostilities’ under the auspices of the International Committee of the Red Cross, and the Tallinn Manual on cyberwarfare prepared at the invitation of NATO. In this article, we discuss the Tallinn Manual, showing how experts faced with uncertainty as to the law's precise scope and meaning construct legal interpretations, legal definitions, and institutional facts and norms that can be used to make sense of a contingent world. At the same time, we argue, this absorption of uncertainty produces new uncertainty. Consequently, the power of experts does not reside in their knowledge, but in their control and management of uncertainty and non-knowledge.