The role of seed producer cooperatives (SPCs) in the Ethiopian seed sector and their contribution to seed supply improvement have received attention from researchers, policymakers, and development partners. However, limited work has been done in reviewing and documenting their involvement in the seed sector development. In this paper, we review and discuss the SPCs in the Ethiopian seed sector. Specifically, we reflect on the contribution of SPCs to improving seed availability and access in the country. The current liberal market system of Ethiopia creates new opportunities for growth as successful enterprises, but also brings new challenges, such as more intense competition for smallholder producers. The government policy encourages SPCs to engage in seed business. We draw on scientific literature, reports, white papers, project documents, and websites. The review reveals that the seed sector in Ethiopia consists of three seed systems: formal, informal, and intermediary seed systems. Each seed system has a specific contribution to the delivery of seed to farmers, but they vary in their approach and respective strategies. The SPCs are categorized in the intermediary seed system because they have features of both formal and informal seed systems. They play a key role in meeting seed demand and contribute greatly to seed supply improvement through high-volume production of seed, crop, and variety diversification, and seed delivery to farmers. They produce and market the seed through various market channels, including direct sales to farmers, sales through contractual agreement, and sales directly to institutional buyers. Their contribution to improving the seed supply and seed security has received considerable recognition by policymakers and development practitioners. Therefore, government and development partners should support and strengthen SPCs to maximize their success in the seed business and their contribution to improving the seed supply in Ethiopia.