This paper presents unique descriptive and explanatory analyses of cross-national variation in work ethic in 44 European countries (European Values Study 2008). A strong work ethic is the conviction that people have a moral duty to work. To explain differences in the adherence of the work ethic between countries two alternative theories are tested: modernisation theory and social institutional theory. Modernisation theory hypothesises that richer, more highly educated and urbanised countries have a weaker work ethic. Alternatively, social institutional theory predicts that countries' religious heritage, generosity of the welfare state and political history can explain differences in work ethic between countries. Multilevel regression models on an unprecedented set of 44 countries show that the modernisation hypotheses are supported. With regard to institutions, it is shown that work ethic is stronger in countries with an Islamic and Orthodox heritage as compared to a Protestant and Catholic heritage and in ex-communist countries and countries with less generous welfare states. When both theories are tested simultaneously, variance decomposition suggests that social institutional theory has more explanatory power than modernisation theory. Religious heritage is shown to be the most important factor to explain variation in work ethic between countries. Thus, although our modern societies become increasingly secularised, religious heritage still impacts our norms and values about work in a significant manner.