This monograph explores how sustainability in textile supply chains can be reconceptualized through a relational perspective. While the textile industry remains a significant driver of global economic growth, it is also among the most environmentally and socially challenging sectors, marked by high emissions, intensive resource consumption, and persistent labor issues such as unsafe and unhealthy working conditions, child labor and gender discrimination. Drawing on the triple bottom line framework, the study argues that advancing sustainability objectives requires collaborative approaches that extend beyond individual firms and embrace inter-organizational dynamics. Within this view, relational learning is identified as a central mechanism through which supply chain actors can enhance sustainability performance. By integrating a comprehensive literature review with an in-depth case study and empirical analysis of the Prato textile district in Italy, the monograph shows how collaboration and relational learning interact to generate environmental, social, and economic benefits.