The thesis seeks to advance the understanding of the ‘energy weapon’, by providing explanations on how and under what conditions states can use energy as a tool in conflicts. The literature on the topic is filled with several controversies, stemming mainly from the divides between realist and liberalist theories in International Relations. Thus, research that may contribute to the debate, -will help us to gain a more profound understanding of International Relations as well. The thesis suggests that the research has generally avoided the ‘hybrid’ mode of conflict when studying these questions. The study concentrates on the context of the Ukraine Crisis, since this conflict has been said to incorporate hybrid characteristics and includes an ‘energy weapon’ in the form of Crimean ‘blackout’ in November 2015. The thesis begins by reviewing the concept of the ‘energy weapon’ itself alongside the theoretical traditions that guide different views. In this part, the thesis also introduces the concepts of ‘hybrid warfare’, ‘energy security’, and ‘securitization’, which help to conduct the analysis. The analysis is conducted through explaining-outcome process tracing studying the period from annexation of Crimea in 2014 to Desember 2015. The findings suggest that the ‘energy weapon’ use and conditions are supported by a variety of factors, some general and some context-specific. The Crimean ‘blackout’ turned out be an instance of ‘energy weapon’, but spurred by non-state actors. However, also several other ‘energy weapons’ were identified during the investigation. The findings suggest that the ‘energy weapon’ turns out to be more of a “shock collar” than a “taser”. Interdependence, mode of conflict, and ‘securitization’ rhetoric are presented as the most important aspects that should be included in the debate on energy as a tool in conflicts.