This is the proceedings of an International workshop on QSO Hosts and their Environments, held on January 10-12, 2001, in Granada, Spain. Advanced technologies in astronomy at various wavelengths have provided us with high resolution and high quality data on the QSO population. This meeting was aimed at understanding the morphology and nature of the host galaxies and environments of QSOs. The invited lectures as well as the contributed and poster papers highlighted the main issues of research: the stellar and gaseous content of the underlying galaxy; the characterization of the population of companions and the nature of their interaction with the host galaxy; the connection between radio-loud QSO and radio-galaxies, and QSOs and ULIRGs; the evolution with redshift of both the host galaxy and its environment, and the main implications in theories of galaxy formation and evolution. This volume provides a valuable overview and timely update of the exciting and rapidly developing field of QSO hosts and their environments - essential reading for graduate students and researchers.