Beef cattle are highly efficient at depositing fat, and they deposit fats in a specific order: first abdominal, then seam (intermuscular), then subcutaneous and finally marbling (intramuscular, interfascicular) fat. The development and composition of these fat deposits are influenced by the diet of the cattle. This chapter addresses the origin of adipocytes, the ontogeny of fat development, factors influencing fat development and, finally, factors influencing fatty acid composition of fat depots.