The purpose of this volume in the Progress in Inflammation Research series is to provide the biomedical and clinical researcher with a state-of-the-art insight in the role of cytokines in joint inflammation and joint destruction. This is of relevance for better understanding of key processes in diseases such as rheumatoid arthritis (RA) and osteoarthritis (OA). Apart from the impact of old and novel cytokines on joint tissues, the various chapters address the issue of targeted therapy with biological response modifiers and future interventions with carefully designed inhibitors. Spe­ cial attention is given to elements of synovial cell activation, cell-cell interaction, cytokine interplay as well as mechanisms of cartilage destruction and bone erosion. In addition to an outline of the role of established cytokines, such as TNF, IL-l and IL-6, new information is given on the novel cytokines IL-15, IL-17 and IL-18 and their positioning in the complex cytokine interplay. Cytokine regulation of destructive enzymes, RANKL, the endogenous inhibitor OPG and their crucial roles as central players in joint erosion are highlighted. Together, the chapters provide a complete and balanced view on pivotal cytokines and joint pathology.