Researchers and policy makers agree that the relation between school and work is an important characteristic of vocational education and training (VET) and needs attention. The relation itself poses several challenges for research to be successful and useful for policy makers. In this article, we outline these challenges and answer the following question: "What needs to be considered when researching the relation between school and work?" Our central claim is that research on the relation between school and work needs to (1) take into account contextual conditions of the VET system, including identifying the central actors and their responsibilities within a VET system, (2) take into account the characteristics of VET itself, (3) define the quality of the relation between school and work (depending on the context, characteristics of the VET system and VET itself), and (4) be consistent with respect to chosen research aims and paradigms. To illustrate how these aspects can be taken into account an example of empirical research conducted in the German dual apprenticeship system is described. The readers are provided with guidelines for researchers and policy makers to carry out high quality research on the relation between school and work in VET systems that enables policy makers to make use of the results to improve the relation between school and work in VET systems.