Insulin resistance is defined as an impaired biological response to either exogenous or endogenous insulin. It is an increasingly prevalent disorder in the developed countries and is known as a high risk factor for both cardiovascular diseases and malignancies. This book describes the endocrine disorders that are associated with changes in insulin sensitivity, often resulting in clinical consequences such as impaired glucose tolerance or secondary diabetes mellitus. The main components of a pathological condition known as metabolic syndrome (MS) or syndrome X is also described, including insulin resistance, type II diabetes, hypertension, central obesity, dyslipidemia, and nephropathy. The treatment of type II diabetes is examined, including the adjustments to changes in insulin resistance and secretion and to variations in basal and prandial glucose along the diabetes continuum. The prevalence of insulin resistance among children and adolescents is also looked at, including insulin resistance in childhood cancer survivors. In addition, the association between insulin resistance and oral cancer risk (i.e. smoking) is addressed, as well as the roles of insulin resistance and sympathetic nerve activity in obesity, hypertension, Turner syndrome and liver disease. The association between non-alcoholic fatty liver disease (NAFLD) and insulin resistance, and the pathogenetic and therapeutic implications are also addressed.