This chapter looks at the processes involved in maintaining stable blood glucose concentrations. It discusses the absorptive and postabsorptive phases of metabolism, the role of insulin in glucose uptake, and the hormones and mechanisms involved in regulating glucose levels during fasting. It also covers the causes and diagnostic approach to hypoglycaemia and hyperglycaemia. Information on differentiating between stress hyperglycaemia and other causes of hyperglycaemia, such as diabetes mellitus, is included.