Objective : The aim of this article is to define and validate the “system is broken” index. The index measures anti‐establishment attitudes cross‐nationally. Methods : Using survey data from 25 countries, we test the reliability of the system is broken index and then demonstrate its convergent and divergent validity. Results : The results reveal that the system is broken index is a reliable and valid measure capturing perceptions that the political system, in any given country, is broken and is not working for the average person. The index predicts related attitudes (nativism and populism) and provides stable estimates of anti‐establishment attitudes over time. Conclusions : The system is broken index helps to predict the conditions that give rise to anti‐establishment candidates and populist movements. Tracking the measure across three decades provides unique insights into the challenges confronting contemporary politics, including the rise of populism movements.