Estimation of active pharmaceutical ingredient is very important because it helps us to know the actual amount of drug present in formulation as per the label claim. It can be achieved by various spectroscopic, chromatographic and hyphenated techniques. Simultaneous estimation of two or more than two drugs in single formulation can be better, cost effective and less time consuming method as compared to analyze drugs individually. In simultaneous estimation, all the active drug materials are determined by using single solvent system, at one time, single equipment and by one analyst also. The main problem in simultaneous estimation is the overlapping of responses of the drug material which is very difficult to resolve by simple conventional techniques. So to overcome these type of problems, chemometric tools has been introduced which can be easily resolve and extract the information from the data obtained by using various univariate or multivariate calibration and validation methods.