Dairy cattle may experience several problems around calving that are correlated with the amount of body fat. Therefore, body condition score (BCS) systems have been developed to help monitor and manage body fat reserves so as to minimize disease, and metabolic and reproductive problems. Use of the BCS system has helped to improve production efficiency and to reduce metabolic and reproductive disease incidence and severity. From the study of the ‘fat cow syndrome’ as a way to define problems with overly fat pregnant animals to the modern concern with increasing feed intake to support genetic ability for milk production, decades of research on body fat have revealed many underlying physiological controls. This research has done much to define the role of body fat in postpartum problems in cows and improve productive efficiency. We manage body fat because of its relationship to metabolic diseases or reproductive problems. The rapid loss of body fat can lead to ketosis, depressed feed intake, furthering ketosis, displaced abomasum, and reduced fertility. Modern research focuses on determining the endocrine and physiological mechanisms of the relationship of body fat to efficiency. A continued integration of basic research and practical application promises to improve the overall health and efficiency of dairy cattle.