Sliding Mode Control is recognized as an efficient tool to design controllers which are robust with respect to uncertainty. The resulting controllers have low sensitivity to plant parameters and perturbations and allow the possibility of decoupling the original plant system into two components of lower dimension. In addition many controllers ensure finite time convergence to the switching surface and can be straightforwardly implemented. However, in addition to this traditional area of exploitation, sliding mode concepts are being increasingly deployed for the design of observers for estimation and identification. Many of the chapters in this book are based on expansions of selected presentations from the 8th IEEE International Workshop on Variable Structure Systems VSS'04, which was held in Barcelona, Spain in September 2004. The editors have tried to identify the key contributions from this workshop, which define the state-of-the-art, represent new directions building on existing work, and highlight new emerging application areas.