The role of the renin-angiotensin-aldosterone system (RAAS) on the development of insulin resistance and type 2 diabetes (T2DM) is an area of growing interest. Most of the deleterious actions of the RAAS on insulin signals appear to be mediated through activation of the serine/threonine kinase, oxidative stress and tissue-inflammation in insulin-sensitive organs. Both experimental and clinical studies demonstrated that angiotensin II (Ang II) and aldosterone could play a role in the development of insulin resistance, diabetes and cardiovascular diseases. Large randomized clinical trials revealed that blockade of the RAAS with either angiotensin I converting enzyme inhibitors or AT1 receptor blockers results in decreased T2DM incidence, with a minor attenuation of markers for insulin resistance. This review focuses on the role of RAAS in the pathogenesis of insulin resistance, as well as on clinical relevance of RAAS blockade in the prevention and treatment of the metabolic syndrome and pre-diabetes.