In the past decades supersymmetric field theories have been the subject of intense research activity and represent an important theoretical laboratory which allows us to investigate the dynamics of strongly-coupled field theories. In particular, recently there has been a huge progress in our understanding of N=2 theories in four dimensions. The scope of this book is on the one hand to provide a review of these new developments and on the other to illustrate what one can learn from these results about intrinsically strongly-coupled phenomena, such as confinement and dynamical symmetry...