Legitimacy is a contested concept in political science. The question of legitimacy has been addressed in various topics, including state formation, state building, and state failure. This research is an attempt to quantitatively test the relationship between state legitimacy and state effectiveness and development in the economy, politics, and society. By examining the literature on legitimacy and its sources, the research tests the following hypothesis: a state with better performance in macro issues, including economic performance, social welfare, and political participation, is more likely to enjoy a higher level of legitimacy. In other words, this study attempts to establish a replicable formula for an incumbent state to achieve and sustain its legitimacy.