In autumn 2002, the Ernst Schering Research Foundation Workshop sponsored the 45th in its series of conferences devoted to emerging areas in basic and applied biomedical research. These conferences bring together a critical mass of top scientists working in an impor- tant area in an intimate setting that fosters the free exchange of knowledge and ideas. In this spirit, Workshop 45 assembled leaders in the field of chemokines - hemotactic cytokines that coordinate leukocyte trafficking - amid the scenic vineyards and wineries of Napa Valley, to discuss the latest concepts of how these molecules regulate the immune response and disease. Chemokines were se- lected as a conference topic because they have revitalized the study of leukocyte trafficking and are widely considered to be potential new targets for drug development, in diseases ranging from acute in- flammation and autoimmunity to HIV and cancer. Discovered in the 1980s, the chemokine superfamily currently has 43 human members, making it the largest subset of cytokines. Mem- bers are defined by conserved sequences and a common three-di- mensional fold, and can be divided into two major functional groups - homeostatic and inflammatory - depending on whether they are produced constitutively, and thereby control basal lymphocyte traf- ficking, or whether they must be induced, for example by pathogens or injury, and thereby control deployment of effector leukocytes in emergencies.