In this article, we present the state-of-the-art on socioeconomic health inequalities with a focus on the Nordic countries. Health inequalities have increased over time and can be observed for both mortality and morbidity. We show that cross-national comparisons reveal surprisingly high inequalities in the Nordic countries. It is now well established that health and mortality inequalities prevail also at older ages. We show, with data from Sweden, that the interpretation of how mortality inequalities evolve over the life course is markedly different depending on whether we focus on absolute or relative inequalities. Although there is a consensus on basic descriptive facts, disagreements on how these facts are best explained and why they persist and even increase remain. We present a general discussion on how to explain health inequalities, as well as a discussion on why patterns may differ between European regions and across the life course. We introduce a framework for understanding health inequalities, fundamental cause theory and discuss to what extent the evidence aligns with the theory. We review contemporary discussions on health inequalities in light of recent evidence based on novel methods for causal inference. We argue that health inequalities have important ramifications for population health regardless of whether they are primarily shaped by social causation or social selection and end by noting that as modern societies aspire to become more meritocratic, it is possible that socioeconomic position becomes increasingly important for health.