This article examines the extent to which changes in the effect of religion on voting in The Netherlands since the 1970s can be explained by ‘bottom-up’ and ‘top-down’ approaches. The first includes religious integration and education. The latter category encompasses the restructuring of the party system and changes in party positions. Hypotheses are tested employing logistic and conditional logistic regression analyses of the Dutch Parliamentary Election Studies (1971–2006) supplemented by data from the Comparative Manifesto Project. Weakening religious integration largely explains the decline of political boundaries between non-religious voters and Catholics and Calvinists. In line with earlier research, the article finds that the creation of a single Christian Democratic Party (CDA) has reduced the religion–vote relationship. However, this merger effect largely disappears after taking into account party positions. Moreover, party positions influence the religion–vote association: the effect of religion on voting increases as religious parties emphasise traditional moral issues in their manifestos.