ACCESS exists to champion the contributions that social scientists make towards tackling environmental challenges, such as climate change, biodiversity loss and pollution. To support this, our ‘Capacity Building’ activities form a core workstream. In September 2023 we hosted our second residential training event targeted at early career social scientists (PhD researchers and postdoctoral researchers) working in any sector. The theme for Summer School 2023 was “Supporting Early Career Climate & Environmental Social Scientists”. Sessions included a mix of keynote-style presentations, interactive workshops, and walk-and-talk sessions. The ACCESS Guiding Principles of Environmental Sustainability, Knowledge Coproduction, and Equality, Diversity & Inclusion (EDI) were embedded in the design and delivery of the event. We assessed Summer School 2023 using two data sources - applicants' characteristics (from the application forms) and delegates' experiences (from the feedback survey). Delegates valued the highly interactive programme, opportunities for peer-peer learning, and the residential setting which enabled time for more informal networking. The diversity of participants – in terms of topic, university, country and discipline – was noted as a strength of the event. Delegates also valued the transdisciplinary nature of the speakers. Overall, the ACCESS Summer School 2023 was a very successful event. The energy and enthusiasm of delegates were palpable across the three days, and their enjoyment was expressed in the overwhelmingly positive feedback received.