IntroductionDevelopments in society, and more specifically in labour markets, such as an ageing workforce, high rates of youth unemployment, skills shortages, and flexicurity have an impact on societal demands on vocational education and training (VET). Employees who are professional, flexible, and employable, who have the necessary competences, and who are capable of lifelong learning (OECD, 2014) are needed. In this regard, VET plays a key role in their preparation. The relationship between school and work is one of the key characteristics that determine the quality of VET. It has received a great deal of attention in the past in political and (inter)national debates (OECD, 2010), as well as in research (Tuomi-Gröhn, Engeström, & Young, 2007). Nevertheless, it still needs improvement. It is a complex issue, where different levels of analysis are often intertwined. These levels include: the context of VET systems (i.e. society); the settings in which VET takes place (e.g. the 'school' and the 'work organisation'); the content of the training; and the knowledge, skills and competences that are provided and acquired in both settings. We argue that, in order to improve the relationship between school and work, we must take into account the characteristics of the system in which this relationship is embedded. A system is defined as 'congeries of interdependent flows and activities linking shifting coalitions of participants embedded in wider material-resource environments' (Scott & Davis, 2007, p. 34). Moreover, the specific characteristics of the relationship between a VET system and the associated school-work relationship determine how it must be researched.Therefore, our central question is: what needs to be considered when investigating the relationship between school and work?In the following sections, we analyse these requirements from three perspectives: (1) the VET system and its contextual characteristics, (2) the school-work relationship in VET at different levels, and (3) the requirements of good and adequate research. Each of these perspectives allows us to derive the unique requirements for researching the relationship between school and work in specific contexts. Based on these results, we discuss implications and guidelines that aim at raising researchers' awareness of the necessary decisions which, in turn, facilitate the quality of research projects which investigate the quality of the relationship between school and work in different VET systems. Moreover, we illustrate our results with a study on the German dual apprenticeship system and draw conclusions about important issues which should be addressed by policy makers.