With the takeover of Crimea by masked Russian soldiers/fighters without national insignia in February/March 2014, with the Kremlin at first denying its involvement, war became ‘hybrid’ in our minds. The follow-on conflict in Eastern Ukraine, with separatism supported by neighbouring countries and the armed establishment and military securing of pseudo-state people’s republics, including recourse to pro-Russian fighters ‘on holiday’, has reinforced the impression of a hybrid form of warfare, raising the question: what is hybrid warfare? This article argues that the specific nature of hybrid warfare is essentially a strategic matter characterised by three key tendencies and their orchestration within a hybrid ‘grand strategy’: 1. Focusing the decision of the war/conflict, as such, primarily on a broad spectrum of non-military centres of gravity in a flexible and dynamic manner. 2. Operating in the shadow of various interfaces against specific vulnerabilities of the opponent, thus challenging traditional lines of order and responsibilities, creating ambiguity and paralysing the decision-making process of the opponent. 3. Creative combination and parallel use of different civilian and military means and methods, categories and forms of warfare and fighting, thus creating ‘new’ mixed, hybrid forms.1 At the same time, there is a growing sense that hybrid forms of warfare will shape the face of war in the 21st century.2 They seem to offer unpretentious political success by smart recourse to limited, deniable and supposedly manageable use of force. The assumption that the risk of military escalation and political damage could be kept within limits may at the same time increase the likelihood of the offensive use of hybrid forms of warfare. For this reason, it is high time to improve our common and comprehensive understanding of hybrid forms of warfare as a precondition for common and comprehensive action in defence and response.