Achieving sustainable production is a critical task in today's globalised world. This is especially the case in the cotton garment industry where globally dispersed suppliers feed rapidly expanding demand across international markets. Practices associated with cotton garment production face numerous sustainability challenges from cotton farming to textile and garment manufacturing. Retailers are under increasing pressure to address these challenges and leading retailers are now actively trying to promote more sustainable production across all stages of production from raw material to final product. While numerous studies have investigated the relationship between retailers and their upper tier suppliers, there is little understanding of how sustainability challenges can be addressed across fragmented production processes. It is this gap that this thesis seeks to fill. Promoting sustainable production from raw materials to the final stages of manufacturing involves influencing practices of a diverse set of businesses responsible for different stages of production. This thesis defines the set of businesses that turn raw materials into final products as an 'extended supplier network' (ESN). Drawing on global value chain (GVC) and global production network (GPN) approaches to understanding how production is organised, the core question of this thesis is: To what extent is buyerdriven governance sufficient for promoting sustainable production across fragmented production processes in an ESN? GVC and GPN research provides insight into this issue as it offers a way to conceptualise how lead firms influence their suppliers. The GVC approach highlights the importance of lead buyers. The GPN approach incorporates this argument but further emphasises the importance of spatiality and the roles of a wider set of actors and processes. While both approaches theoretically incorporate all stages of production, garment industry studies using these approaches have tended to focus on relationships between brands and retailers and upper tier suppliers, paying insufficient attention to lower tiers. Considering the case of Indian cotton clothing production for major UK retailers, this study explores retailers' governance relationships with producers at different points in their ESNs. Producers' experiences of vertical governance through buyer-seller relationships across all stages of production within an ESN are explored. These producers' experiences with horizontal governance within distinct local productive systems are also considered. Diverse producers' locations within the ESN and within local productive systems are found to involve different governance experiences within the same ESN. Across the ESN, vertical governance flows are found to be limited by variation in potential for buyer governance across buyer-seller relationships in the multiple vertical pathways connecting retailers to raw material producers. Alternatively, retailers can connect to producers by making non-sourcing horizontal connections with actors in local productive systems. While dominant methods in retailers' efforts at governance for sustainability have been vertical, horizontal connections are increasing across the industry. However, despite the emergence of new connections, this research finds that retailers' influence over lower tier production processes remains limited. Empirically, this thesis provides insight into the complexity of sustainability challenges involved in the production of cotton garments. Conceptually, it shows the nature of diverse governance relationships across an ESN. It also emphasises that effective governance for sustainability cannot be achieved simply through vertical buyerdriven governance. Instead a more nuanced, and more complex, understanding of the interplay between vertical and horizontal is required, particularly considering the role of alliances. This has significant implications for policy, including the public and private governance for sustainability in the global cotton garment industry.