This monograph demonstrates that adopting a relational sociology perspective provides both theoretical clarity and practical insight into sustainable supply chains. By reframing supply chains as networks of interacting actors, it shows that sustainability stems less from individual firm choices than from processes of relational learning and joint sense-making. Empirically, the Prato textile district illustrates how trust-building, joint problem-solving, and relational capital strengthen sustainability and competitiveness. At the same time, the study acknowledges limitations and opens avenues for future research, including the need to test the relational learning model in diverse contexts and to examine how digital traceability technologies interact with inter-firm collaboration.