The rise of violent non-state actors (VNSAs) has become a feature of international security in the past few decades. Despite enormous efforts from the academic, policy and intelligence community, VNSAs have proven remarkably difficult actors to engage with or defeat. This thesis applies the strategy of coercive diplomacy to the VNSA problem and argues it provides policymakers a useful option for countering VNSAs. The thesis incorporates findings from fields as diverse as international relations, history, psychology and behavioural economics to provide an understanding of coercer and VNSA behaviour under coercive diplomacy situations. The primary aim of this thesis is to construct a framework of factors that heighten coercive diplomacy's probability for success against VNSAs. These factors are (1) an asymmetry of motivation in favour of the coercer; (2) credible threats and objectives; (3) the support of others and (4) incentives. Implementation of the framework does not guarantee a successful outcome as coercive diplomacy is a highly contextual strategy that can deliver vastly different results in varying circumstances. To demonstrate the importance of context this study tests the framework against two case studies. The first considers the British government's coercive diplomacy strategy against the Provisional Irish Republican Army and argues that coercive diplomacy was successful owing to a strategy that conformed to the framework. The second is a test-case that examines the feasibility of a US led coercive diplomacy strategy against the Islamic State, arguing that it is an example of the limitation of coercive diplomacy against VNSAs. These case studies demonstrate that coercive diplomacy has important implications for countering VNSAs in the future. While coercive diplomacy will not be a suitable strategy in some circumstances, to date it has been vastly underutilised.