Seed composition is crucial for the efficacy of soybeans [Glycine max (L.) Merr.] used in food, feed, and fuel. Soybean breeders strive to improve protein, oil, fatty acid, amino acid, and carbohydrate contents in soybean seeds while increasing yield. Negative relationships between protein content and both yield and oil content present challenges for breeders. Environment also affects the accumulation of seed components. Various approaches were taken to understand seed composition traits in relation to yield and environment and to determine the ability to manipulate these traits genetically to produce desirable soybean germplasm. Fast neutron mutants in elite backgrounds and a near-isogenic elite line with a high-protein introgression were utilized to further the understanding of seed composition and yield in southern soybean lines and to develop resources for improvement of seed composition in soybean.