Chemometrics is the chemical discipline that uses mathematical, statistical and other methods employing formal logic: to design or select optimal measurement procedures and experiments, and -- to provide maximum relevant chemical information by analysing chemical data. Being conceived as a branch of analytical chemistry, chemometrics now is a general approach. It extracts relevant information out of measured data, regardless of their origin: chemical, physical, biological, etc. Chemometrics has been applied in different areas, and most successfully in multivariate calibration, pattern recognition, classification and discriminant analysis, multivariate modelling, and monitoring of processes. The main chemometric principle is a concept of hidden data structures that can be found using methods of multivariate data analysis. These are the well-known statistic tools such as partial least squares (PLS), soft independent modelling of class analogy (SIMCA), principal-component regression (PCR), wavelet analysis, and many others. Current activities of chemometricians fall into two main categories: (1) development of new methods for manipulating multivariate data and (2) new applications of the known chemometric techniques in different areas such as environment control, food industry, agriculture, medicine, and engineering.