Russia’s use of force against Ukraine since early 2014 has prompted some observers to remark that it is engaging in ‘hybrid warfare’. This form of military statecraft has made other former Soviet republics, such as the Baltic countries, fear that Russia would use subversion rather than pursue a conventional military engagement against them. Despite this concern about Russian hybrid war, existing descriptions of this form of war suffer from conceptual weaknesses. In this article hybrid warfare is conceived as a strategy that marries conventional deterrence and insurgency tactics. That is, the belligerent uses insurgent tactics against its target while using its conventional military power to deter a strong military response. The article then outlines why some former Soviet republics are susceptible to Russian hybrid warfare, allowing it to postulate inductively the conditions under which hybrid warfare might be used in general. The analysis yields two policy implications. First, military solutions are not wholly appropriate against hybrid warfare since it exploits latent ethnic grievances and weak civil societies. Second, only under narrow circumstances would belligerents resort to hybrid warfare. Belligerents need to be revisionist and militarily stronger than their targets, but they also need to have ethnic or linguistic ties with the target society to leverage in waging hybrid warfare.