Military coups happen for various political, economic, and historical reasons. A vast literature investigates the external factors that affect coup vulnerability, including interstate wars, security threats, regional spillovers, and foreign economic linkages. An even more impressive number of studies, going back almost seven decades, focuses on the domestic causes of military coups. These causes of coups can be classified under two broad headings: background causes and triggering causes. Background causes are those structural determinants that generally increase coup vulnerability in a given country and create motives for coup attempts. The most prevalent background causes concern the regime type and characteristics, historical legacies and cultural diversity, and economic conditions. The triggering causes are temporally and spatially more specific conditions that determine the opportunities for coup plotters. Various types of political instability and violence, such as popular protests and civil wars, can become important triggers. Additionally, the characteristics of the military organization and the effectiveness of coup-proofing strategies fall under this category. An extensive review of the cross-national civil-military relations literature reveals that very few of the proposed determinants survive empirical scrutiny. Three findings stand out as consistently robust predictors of coup activity. First and most notably, there is broad consensus that the “coup trap” is an empirical reality: coups breed coups. This finding is bolstered by the fact that military regimes are especially vulnerable to coup attempts. Second, income and wealth have a strong negative correlation with coup probability. All else equal, poor countries are more coup prone than their richer and more developed counterparts. Last but not the least, political instability and violence increase coup likelihood, although scholars differ on which exact type of instability or popular unrest is the most significant. Many other oft-cited factors such as colonial legacy, culture, ethnic fractionalization, resource wealth, and economic crisis are not consistently robust in global samples. This observation highlights the need for more metastudies to separate the relevant variables from idiosyncratic effects.