Most of the existing literature on the determinants of terrorism treats terror as a uniform phenomenon and does not distinguish between different types of terror. We argue that terror groups of different ideological types should be affected by different determinants as they cater to different grievances, engage in compromise to differ- ent degrees and have different organisational constraints. We explicitly address the heterogeneity of terror by classifying groups according to their ideologies and, using the Global Terrorism Database, show that the determinants of terror differ strongly between terror types.