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This study examines the influence of different forms of proximity (cognitive, social, institutional and geographical) on the absorptive capacity of purchasers in adopting eco-innovative practices. Drawing on the dynamic capabilities framework and the Proximity School, it draws on case studies of 11 eco-innovation projects. Although the study is cross-sectional, the professional seniority of many respondents provides a longitudinal perspective. The results show that cognitive proximity promotes the sharing of technical knowledge and understanding of processes. Social proximity strengthens trust and interpersonal cooperation, facilitating the exchange of tacit information. Institutional proximity aligns actors around common reference points such as standards and labels. Finally, geographical proximity facilitates direct interactions and supports short circuits. This work thus sheds light on the relational levers that favour the ecological transformation of purchasing organisations by highlighting the combined and evolving effect of different forms of proximity.