Context: Place-based transdisciplinary research involves multiple academic disciplines and non-academic actors. Long-Term Socio-Ecological Research (LTSER) platform is one concept with ~ 80 initiatives globally. Objectives: As an exercise in learning through evaluation we audited (1) the siting, construction and maintenance of individual LTSER platforms, and (2) them as a distributed infrastructure for place-based transdisciplinary research with focus on the European continent. Methods: First, we defined a normative model for ideal performance at both platform and network levels. Second, four surveys were sent out to the 67 self-reported LTSER platforms officially listed at the end of 2016. Third, with a focus on the network level, we analyzed the spatial distribution of both long-term ecological monitoring sites within LTSER platforms, and LTSER platforms across the European continent. Fourth, narrative biographies of 18 platforms in different stages of development were analyzed. Results: While the siting of LTSER platforms represented biogeographical regions well, variations in land use history and democratic governance were not well represented. Platform construction was based on 2.1 ecological monitoring sites, with 72% ecosystem and 28% social system research. Maintenance of a platform required three to five staff members, focused mostly on ecosystem research, was based mainly on national funding, and had 1–2 years of future funding secured. Networking with other landscape approach concepts was common. Conclusions: Individually, and as a network, LTSER platforms have good potential for transdisciplinary knowledge production and learning about sustainability challenges. To improve the range of variation of Pan-European social–ecological systems we encourage interfacing with other landscape approach concepts.