These notes are based on the material presented in a series of lecΒ tures in the IBM Systems Research Institute (ESRI) in Geneva durJng 1967-1969 to systems engineers working in the design and programming of computer systems for control and monitoring of i~nustrial procΒ esses. The purpose of the lectures and this book is to give a survey of difΒ ferent approaches in developing models to describe the behavior of the process in terms of controllable variables. It does not cover the theory of control, stability of control systems, nor techniques in data acquisition or problems in instrumentation and sampling. But certain aspects in the organization of data collection and design of experiments are obtained as side products, notably the concept of orthogonality. The reader is assumed to have a working knowledge of elementary probΒ ability theory and mathematical statistics. Therefore, the text conΒ tains no introduction to these concepts. The author is aware of some inaccuracies in not making proper disΒ tinction between population parameters and their sample estimates in the text, but this should alw~s be evident from the context. The same applies to the occasional replacement of number of degrees of freedom by the number of samples in the data. In practice, computer collected sets of data consist of a high number of samples and the difference between the two is inSignificant.