The overarching aim of this chapter is to investigate how sustainability practices emerge, diffuse, and consolidate within industrial supply chains, and to assess the role of collaboration, relational learning, and network embeddedness in shaping these processes. While much of the existing literature in supply chain management and organizational studies has examined sustainability either through quantitative surveys, our objective is to combine theoretical depth with empirical richness to understand the mechanisms through which firms adopt and co-create sustainable practices. This section aims to respond to this research question: how do collaborative relationships and relational learning processes shape the trajectory of sustainability in industrial districts? By analyzing the Prato textile district in Tuscany, Italy, the chapter explores the micro-dynamics of how sustainability is developed. It investigates the ways in which suppliers, manufacturers, retailers, and intermediaries interact to negotiate compliance, develop innovations, and promote relational learning such as trust, shared knowledge, and a collective sense of responsibility. First, we seek to map the actual practices and relational processes through which firms respond to sustainability challenges. Second, we aim to generate a set of insights that will inform the design of the subsequent quantitative phase of the research. In line with the sequential mixed-methods design of the monograph, the findings function as contributions and methodological building blocks for the survey instruments that follow. We analyzed the interview data using thematic analysis. This approach allows us to verify whether anticipated constructs appear, while also remaining open to new, unexpected themes. By blending deductive structure with inductive openness, we aim to capture both expected and novel dynamics.