The burden of ill health and the blessing of good health are unequally distributed in society. The lower strata - those with hard jobs, modest wages and low education - have higher mortality and more morbidity than the more privileged strata. This issue reflects the injustices prevailing in modern society and constitutes a major challenge for public health. In recent decades, the topic of social inequalities in health has been addressed by a growing body of research. This thesis, submitted for the degree of dr.philos. at the University of Oslo, presents a sociological perspective on how such health inequalities can be explained. It gives a comprehensive review of the main theoretical alternatives and contributes to the on-going empirical research with five original articles.