The main purpose of any chromatographic analysis is to resolve mixtures of compounds into less complex mixtures or ultimately into pure components. In addition to this function, the chromatographic system can provide retention data which serve as complementary information for the positive identification of resolved components. The need to express gas chromatographic retention data in a standardized system has long been recognized and retention index values presented to be a valuable parameter. Those values are mainly calculated by applying the equations proposed by Kováts, for isothermal analysis, and van den Dool and Kratz, for programmed gas chromatographic runs. In general, these indices denote the retention behaviour of the compounds of interest according to a uniform scale determined by a series of closely related standard substances. The use of retention indices in the flavour and fragrance field is well-documented, and they are widely applied for the comparison of results between laboratories, as well as to characterize stationary phases. Copyright © 2008 John Wiley & Sons, Ltd.