The multivariate optimization designs most used in analytical chemistry are presented, with a particular focus on the Modified Simplex Method. The sequential movements for this procedure are described in detail by means of an hypotetical example and its application is discussed by using a 3-variable chemical system, where the analytical response, taken as the difference in absorbance, Delta A, due to the absorbance readings of the Mo(VI) catalysed and non catalysed (blank) oxidation of iodide ions with hydrogen peroxide in acid medium, are related to the concentrations of the reagents involved, Other examples from the literature are also cited.1912429