The practice of rebel diplomacy is essential for violent non-state actors on the verge of new statehood or seeking legitimacy for a new regime. But effective diplomacy can serve a number of critical purposes during wartime as well. In the short term, external ties may provide material resources, training, or otherwise martial support to alter the course of fighting on the ground. Over the longer term, establishing bilateral relations with third parties, concluding trade agreements, or being allowed to participate in cease-fire or settlement negotiations can lock in strategic advantages that are difficult to overturn. Rebels face significant barriers to utilizing diplomacy, however. Some are inherent to the nature of the international system, some are erected by the embattled governing regime, and still others are endemic to rebel organizations themselves. This chapter introduces the important – and so far neglected – topic of rebel diplomacy in wartime. I argue that we can only hope to understand contemporary civil war by better understanding the interplay between violent and non-violent tactics