Insulin resistance is an essential metabolic phenomenon that plays an important part in the pathophysiological development of a number of common diseases, such as obesity, type 2 diabetes, arterial hypertension, polycystic ovary syndrome, Alzheimer's disease, fatty liver disease, and several types of cancer. It is therefore important for the clinician to understand the nature of insulin resistance. The purpose of this article is to provide a status of today's knowledge on the subject that applies to diagnosis and treatment of patients with insulin resistance in the daily clinic.