District heating systems (DHS) serve as promising infrastructures to harness renewable energy for space heating and domestic hot water purposes. However, the manner in which the potential of renewable energy sources (RES) is assessed varies across sources. This study aims to synthesise knowledge on methodologies for evaluating the integration of various RES into DHS. Key aspects scrutinised in the methodologies include the dimensions addressed, the spatial approaches used, the tools and methods applied, and the overall process followed. A structured literature review process was conducted, reaching 260 documents for full-text review, encompassing scientific publications, national comprehensive assessments, and project reports. The focus has been put on six RES: heat sources for heat pumps (HPs), solar thermal, geothermal heat, biomass, power-2-heat (P2H), and surplus heat. The review highlights surplus heat as the most frequently studied source (35%). Moreover, it shows that from a technological point of view, HPs constitute an indispensable element in integrating most RES (except biomass), particularly in next-generation DHS where reduced supply temperatures enhance HP efficiency. From a methodological perspective, it is observed that spatial mapping is increasingly utilised to deal with the dispersed nature of heat sources and demands. The findings also accentuate the necessity of sector coupling to provide a holistic analysis, given either the inherent interlinkages between the DH sector and others (e.g., in P2H), the derivation of heat from other sectors (e.g., surplus heat), or the multifunctionality of certain heat sources (e.g., geothermal and biomass). © 2025 The Authors