sentences: The topic of cyber warfare is a vast one, with numerous sub topics receiving attention from the research community. We first examine the most basic question of what cyber warfare is, comparing existing definitions to find common ground or disagreements. We discover that there is no widely adopted definition and that the terms cyber war and cyber warfare are not well enough differentiated. To address these issues, we present a definition model to help define both cyber warfare and cyber war. The paper then identifies nine research challenges in cyber warfare and analyses contemporary work carried out in each. We conclude by making suggestions on how the field may best be progressed by future efforts. © 2014 Elsevier Ltd. All rights reserved.