Category and inventory management in retailing involves many novel and challenging aspects, including shelf space allocation, effect of inventory on stimulating demand, retail competition, substitution, and transshipment. Suitably managing these aspects has required new modeling advancements in the operations research and management science literature with the potential for a large improvement in the profitability of retailers. In this introductory article, we describe the main characteristics of these models, focusing on the principles involved, the insights from optimization, and techniques or heuristics used in practice.