This study gathers knowledge and formulates policy recommendations to optimize the large-scale implementation of shallow geothermal systems in Flanders, supporting the Flemish energy and climate policy. The study addresses three core aspects. First, it characterizes the thermal conductivity of the Flemish subsurface by compiling a comprehensive dataset and conducting a detailed analysis of measurement data and literature. The outcome of this section includes spatial maps depicting the average thermal conductivity of the subsurface in Flanders. Second, the study examines the impact of a high density of geothermal systems, with a focus on interference risks and potential effects on the ecosystem services provided by the subsurface. This analysis is based on literature review, real-world case studies, spatial assessments, and both analytical and numerical modeling. Third, the study evaluates the implementation of collective geothermal systems in Flanders through five case studies, outlining the technical, financial, organizational, and legal conditions required for successful deployment. This section also includes a spatial analysis, assessing the potential of undeveloped land in Flanders to supply geothermal heat to specific areas. For each of these topics, the study formulates concrete policy recommendations.