This thesis explores how small and medium-sized enterprises (SMEs) in the Swedish sustainable fashion sector address challenges in sourcing sustainable materials. The aim is to understand the strategies, constraints, and adaptations that enable these businesses to operate under limited resources while maintaining sustainability commitments. A qualitative research design was applied, using semi-structured interviews with four Swedish fashion SMEs that incorporate sustainable sourcing into their business models, including upcycling and ethical sourcing. The findings reveal that sourcing practices often rely on second-hand materials, donations, and smallscale suppliers, with a preference for natural fibers such as linen, cotton, silk, and hemp. Verification of sustainability claims is commonly based on trust, visual inspection, and informal testing, as access to formal certification is limited. Key challenges include inconsistent material availability, high costs of certified fabrics, and supply chain risks when working with international artisan producers. Despite these obstacles, SMEs adapt by using upcycling, small-batch production, and transparent communication with customers to build trust and brand identity. The study contributes to the understanding of sustainable sourcing in resource-constrained contexts and highlights opportunities for policy and industry support to strengthen SMEs’ ability to source sustainably.