Résumé : 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 general practitioner is not mandatory in Belgium), to general practice research networks and computerisation. It could be shown (1) that Belgium has held a middle position in the European Union regarding GP computerisation; (2) that, contrary to the Netherlands, an operational national GP network based on data from electronic health records (EHRs) could not be established; and (3) that Belgian health system computerisation, which advanced substantially in the last decade, put the issue of health data collection and storage by a new digital service on the agenda. Subsequently, three sub-chapters focus on the development of the three GP networks from their foundation until today. They demonstrate that the SGP and Intego were founded as innovative tools originating from Flemish general practice research, whereas the Monitoring Chart originated from the dynamism of Integrated Primary Health Care Centres (IPHCCs, Maisons médicales) in French-speaking Belgium. Acting as health observatories was both part of the mission of the IPHCCs and the demand of the Regional governments. With time, the research designs of the three GP networks became more sophisticated. Furthermore, European cooperation of the SGP with other GP networks since the late 1980s stands out, since the vision to establish a European sentinel general practice network led to joint influenza surveillance as one of its lasting achievements. In continuation of the developments described above, the second main part of the thesis addresses the missions and the organisation of the three GP networks today as well as their respective strengths and limitations in comparative perspective. It is based on network publications and reports, relevant websites and informal information from the networks themselves. The comparison shows that there is little overlap between the activities of the three GP networks, given the different areas of investigation and the complementarity of supplementary information collected by the SGP versus routine data extraction from EHRs in the other two networks. Furthermore, Intego and the Monitoring Chart essentially cover different parts of the country. The prospective research design of the SGP allows formulating hypotheses and designing research questionnaires with precise definitions of diagnoses before the start of a new research topic in order to minimise inter-observer variability, whereas the diagnosis in the other two networks is the result of the general practitioner's clinical judgement. The Intego network disposes of a substantial number of routine parameters collected over more than two decades by now. With these data, the researchers can design retrospective cohort studies without recording or recall bias by the GP who does not know during his/her daily routine for which research questions his/her data may be used later. The Monitoring Chart stands out by its comparatively strong presence in the Brussels-Capital Region and its data from the less well-to-do part of the population. The third main part of the thesis focuses on STIs which provided a research opportunity, given that Belgian public health efforts to control them have increased in recent years and that the three GP networks engaged in research activities in this regard. The first sub-chapter addresses challenges for the surveillance and monitoring of STIs due to the nature of the pathogens, followed by a sub-chapter about characteristics of STI surveillance and monitoring in Belgium. Afterwards, a sub-chapter describes health policy efforts in order to establish the Belgian HIV Plan 2014-2019. The development of the HIV Plan was analysed by applying the policy streams model of John Kingdon. The analysis was based on published government statements, parliamentary documents, and websites of stakeholders, and showed that the Federal Ministry of Health initiative to achieve the HIV Plan was characterised by a coordinating role with a participatory approach towards the other Belgian governments and stakeholders. The 2013 protocol agreement of the Belgian governments committed them to principles, actions, and cooperation regarding HIV prevention, testing, treatment of persons living with HIV and care for their quality of life, but not to budgets, priorities or target figures. The implementation of the plan, highlighting aspects relating to general practice, is addressed in the subsequent sub-chapter. Two further sub-chapters are based on the analysis of retrospective cohort studies with Intego data from 2009 to 2013, based on EHR routine registration by over 90 general practitioners in Flanders. In the first sub-chapter, the frequencies of gonorrhoea and syphilis diagnoses were investigated. Case definitions were applied. Due to small case numbers obtained, cases were pooled and averaged over the observation period. Frequencies were compared with those calculated from mandatory notification. A total of 91 gonorrhoea and 23 syphilis cases were registered. The average Intego annual frequency of gonorrhoea cases obtained was 11.9 (95% Poisson confidence interval (CI) 9.6; 14.7) per 100,000 population, and for syphilis 3.0 (CI 1.9; 4.5), respectively, while mandatory notification was calculated at 14.0 (CI: 13.6, 14.4) and 7.0 (CI: 6.7, 7.3), respectively. In spite of limitations such as small numbers and different case definitions, the data suggests that the general practitioner was involved in the large majority of gonorrhoea cases, while the majority of new syphilis cases did not come to the knowledge of the general practitioner. The second sub-chapter deals with the prescription of antibiotics to treat gonorrhoea in general practice in Flanders 2009-2013. Belgian guidelines recommended ceftriaxone or alternatively spectinomycin from 2008 onwards and azithromycin combination therapy since 2012. The study investigated to which extent contemporary gonorrhoea treatment guidelines were followed. Ninety-one gonorrhoea cases with ten chlamydia and one genital trichomonas coinfections in 90 patients were registered between 2009 and 2013. The proportion of cases with ceftriaxone and/or spectinomycin prescriptions rose from 13% (two of 15 cases) in 2009 to 56% (nine of 16 cases) in 2013. Combination therapy of ceftriaxone and/or spectinomycin together with azithromycin rose from 0 of 15 cases (0%) in 2009 to 7 of 16 cases (44%) in 2013. Although numbers are small, the results suggest that gonorrhoea therapy guideline adherence improved between 2009 and 2013. Future opportunities, recommended in the final discussion, include (1) extending provider-led STI testing in Belgium, with a prominent role for general practitioners; (2) investigating barriers and facilitators for the achievement of the Global Medical File, notably if sensitive and potentially stigmatising issues such as STIs or mental health are involved; (3) making task delegation by the general practitioner towards other primary health care providers more attractive; (4) facilitating general practitioners' tasks by the introduction of support features into the EHR in order to improve registration and quality of care in general; (5) eliciting Regional government support in order to investigate the diagnostic profiles of the patient population of IPHCCs; and (6) establishing an extended network for the collection and analysis of "production data" (such as the number of contacts, interventions, referrals, prescriptions and diagnostic requests) from general practitioners and other primary health care providers, proceeding from the know-how and the experience of the three investigated GP networks.