This chapter analyzes supply as the structural foundation of retail performance. Aldi’s disciplined sourcing model illustrates how simplified assortments, long-term partnerships, and strict onboarding shape efficiency, quality, and price competitiveness. Four guiding questions define supply strategy: what to sell, who supplies it, how compliance is ensured, and how risks are managed. In addition to cost, sourcing decisions can be based on data like quality metrics and sustainability scoring. Broader issues include sustainability, traceability, circularity, and social impact, which increasingly influence both policy and consumer expectations. Supply becomes a system balancing cost, agility, ethics, and risk.