This volume gathers a number of selected contributions from the XIX Sitges Conference on "Jamming, Yielding, and Irreversible Deformation in C- densed Matter", held at Sitges (Barcelona, Spain) from 14-18 June, 2004. The contributions collected in this volume provide a general overview of the "state of the art", and of the recent developments, in the ?elds of material yield and irreversible deformation in di?erent physical systems, which are of great interest within the realm of Condensed Matter Physics. The Conference was sponsored by several institutions that generously provided ?nancial support: Ministerio de Educaci' on y Ciencia of the Sp- ish Government, AGAUR of the Generalitat de Catalunya, Universitat de Barcelona, and the Centre Especial de Recerca (CER) F' ?sica de Sistemes Complexos. As in former editions of the Conference, the city of Sitges allowed us to use the beautiful Palau Maricel as the lecture hall. We thank them for their kind hospitality. We are also very grateful to all those who collaborated in organizing the event: M. Naspreda, A. P' erez-Madrid, R. Pastor-Satorras, and S. Zapperi.
Finally, we wish to express our gratitude to all the speakers and parti- pants in the Conference, who contributed with high scienti?c level presen- tions, and created a very pleasant atmosphere.