Analyzing data obtained from the literature and our own calculations, significant differences were found among countries in their levels of class voting. The Scandinavian countries had the highest and Canada and the USA the lowest levels of class voting. Since the 1950s, there was a decline in almost all countries in the level of class voting. In this article, several hypotheses were deduced from a limited number of individual assumptions, each purporting to explain the differences among and declining trends within countries. Testing these hypotheses with multilevel techniques revealed that differences among countries can best be explained by their population's religious–ethnic–linguistic diversity, and by the union density within countries. The decline in most countries can best be explained by the rise in their standard of living. Furthermore, a rise in the percentage of union members, especially among the nonmanual classes, accelerated the decline in the level of class voting in some countries.