Insulin resistance is the core metabolic abnormality in type 2 diabetes. Its high prevalence and its association with dyslipidemia, hypertension, hyperinsulinemia, and high coronary and cerebrovascular mortality put it in the forefront as the plausible target for aggressive intervention. Measurements of insulin sensitivity provide clinicians and clinical researchers with invaluable instruments to objectively evaluate the efficiency of both current and potentially useful interventional tools. Although several methods had been developed and validated to evaluate insulin sensitivity, none of these methods can be universally used in all patients. Nonetheless, a method suitable for use in clinical or basic research may not necessarily be a practical method for use in clinical practice or for epidemiologic research. We reviewed the currently used methods for assessment of insulin sensitivity. For each method, we summarized its procedure, normal value, cut-off value for defining insulin resistance, advantages and limitations, validity, accuracy for each patient population, and suitability for use in clinical practice and in research settings. The methods reviewed include fasting plasma insulin, homeostatic model assessment, quantitative insulin sensitivity check index, glucose-to-insulin ratio, continuous infusion of glucose with model assessment, indices based on oral glucose tolerance test, insulin tolerance test, and the so called “gold standard” methods, the hyperinsulinemic euglycemic clamp and the frequently sampled-intravenous glucose tolerance test.