This thesis is devoted to general practice (GP) networks in Belgium, their development and their activities within the Belgian health system context. These networks are specific research tools for the repeated or continuous collection and analysis of data related to diseases and other health events observed in general practice, including interventions of general practitioners. The thesis focuses on three not-for-profit general practice research networks which are operational today: (1) the national Network of Sentinel General Practices (SGP), coordinated by the Federal research institute Sciensano; (2) the Flemish Intego network, coordinated by the Academic Center for General Practice of Catholic University Leuven; (3) the network of the Fédération des maisons médicales et des collectifs de santé francophones (FMM) with its Monitoring Chart (Tableau de bord), which collects data from Wallonia and the Brussels-Capital Region. The thesis is divided into a general introduction, three main parts and a final discussion with concluding remarks. The general introduction outlines the importance of data from general practice and the contribution of GP networks to research. Furthermore, it points out the importance of general practice for the control of sexually transmitted infections (STIs), a specific field of action. The first main part of the thesis investigates the research question of how the three GP research networks developed within the specific context of the Belgian health system. It is based on the interpretation of written sources such as project reports, annual network reports, research publications, parliamentary documents, relevant websites and the existing research literature. The context analysis included a comparison with the Netherlands since the latter have strong traditions with regard to the position of the general practitioner in the health system (gatekeeper to secondary care, whereas in Belgium the patient generally chooses his/her health provider, and a Global Medical File administered by the ...