Different groups of people act in different ways that may affect their health. This may be explained by two mechanisms. Whereas the causation mechanism suggests that people’s socio-economic and socio-demographic positions cause changes in health behaviors, the selection mechanism states that those who behave unhealthily sort into certain socio-economic and socio-demographic positions. In this project, we try to understand these mechanisms by studying what impact life-course transitions, such as divorcing or becoming unemployed, have on health behaviors. We use longitudinal data from the Lifelines study to investigate how life-course transitions impact health behaviors alongside more stable socio-economic characteristics.