System identification is the art and science of building mathematical models of dynamic systems from observed input-output data. It can be seen as the interface between the real world of applications and the mathematical world of control theory and model abstractions. As such it is an ubiquitous necessity for successful applications.

The area has many facets and there are many approaches and methods. The presentation aims at both giving an overview of the "science" side, i.e. basic principles and result and at illustrating the practical, "art", side of how to approach a real problem.

System identification is a very large topic, with different techniques that depend on the character of the models to be estimated, linear, non-linear, hybrid, nonparametric etc. At the same time, the area can be characterized by a small number of leading principles, e.g. to look for sustainable descriptions by proper trade-offs in the triangle of model complexity, information contents in the data, and effective validation.

Lennart Ljung received his PhD in Automatic Control from Lund Institute of Technology in 1974. Since 1976 he is Professor of the chair of Automatic Control in Linkoping, Sweden, and is currently Director of the Strategic Research Center "Modeling, Visualization and Information Integration” (MOVIII).

He has held visiting positions at Stanford and MIT and has written several books on System Identification and Estimation. He is an IEEE Fellow, an IFAC Fellow and an IFAC Advisor as well as a member of the Royal Swedish Academy of Sciences (KVA), a member of the Royal Swedish Academy of Engineering Sciences (IVA), an Honorary Member of the Hungarian Academy of Engineering and a Foreign Associate of the US National Academy of Engineering (NAE). He has received honorary doctorates from the Baltic State Technical University in St Petersburg, from Uppsala University, Sweden, from the Technical University of Troyes, France, from the Catholic University of Leuven, Belgium, and from Helsinki University of Technology, Finland. In 2002 he received the Quazza Medal from IFAC, in 2003 the Hendryk W. Bode Lecture Prize from the IEEE Control Systems Society and he is the recipient of the IEEE Control Systems Award for 2007.