Leadership studies research reveals that political leaders' beliefs affect their political and policymaking behaviour, especially in times of crisis. Moreover, the level of flexibility of these beliefs influences the likelihood that groups of leaders come to collective decisions. Insight into when and why political leaders do, in fact, change their beliefs is sorely lacking. This paper uses fuzzy-set Qualitative Comparative Analysis (fsQCA) to examine the antecedents of belief changes among 12 European leaders, all working in the realm of economic policy. Its findings reveal how increases in unemployment and unsustainable debt, as well as different government ideologies and increases in Euroscepticism lead to economic belief changes. In so doing, this paper begins to open the 'black box' of when, why, and under what conditions leaders change their beliefs. KEYWORDS Beliefs; Eurozone; crisis; European Council; political leadership; QCA Progress is impossible without change; and those who cannot change their minds, cannot change anything. (Shaw 1944: 330) Political leaders, like all of us, are sense-making machines. When faced with a situation that threatens the status quo, political leaders turn to their personal beliefs to make the threat more 'explicable, manageable and actionable' (Blyth 2002: 10). In times of crisis, in particular, political leaders' beliefs inform and shape their policymaking (Cuhadar et al. 2017; Dyson 2018; Kaarbo 2018; Van Esch and Swinkels 2015). At the same time, these beliefs are themselves susceptible to influence from the dynamics of political and economic contexts, a leader's traits, the political CONTACT Marij Swinkels