Workshops on the mechanisms of B cell neoplasia have been organized alternatively in Bethesda and Basel since 1983. Prog­ ress in our understanding of the development and responses of B lymphocytes is presented and discussed with the aim and hope to understand what might go wrong when B lymphocytes are transformed into malignant cells. Such knowledge might lead to better diagnosis, prevention and even cure of these terri­ ble diseases. The presentations at the Bethesda workshops are published as papers in volumes of Current Topics in Microbiol­ ogy and Immunology, while the presentations and discussions in Basel were transcribed and published in Editions Roche. For the first time, a Basel workshop (held 4th-6th October 1998) that has been recorded and, in part, transcribed is being published as papers and discussions within Current Topics. This volume is the latest of a long series which documents the excitements of ground-breaking discoveries as well as the frustrations of our inability to fully understand the mechanisms leading to B cell neoplasia. The papers at the workshop are presented when possible in the sequence in which they were given. However, to facilitate the organization and reading of the book and to highlight gen­ eral topics and themes, the papers are organized into five sec­ tions: I B Cell and Plasma Cell Development II Chemokines and Chemokine Receptors III Chromosomal Translocations, DNA Rearrangements and Somatic Hypermutations IV Biology of Lymphomagenesis, B-CLL, Autoimmunity V Myeloma, Plasmacytomas and Related Subjects.