The papers in this book were presented at the 6th Workshop on Mechanisms in B-Cell Neoplasia, held in Bethesda, March 23-25, 1988. On alternate years this meeting is sponsored by the . ;. Basel Institute of Immunology in Basel, Switzerland and by the National Cancer Institute in Bethesda, and is attended by 100 to 150 parti­ cipants. This 6th workshop, like the preceding five, was characterized by intense and enthusiastic discussion which reflects, we think, the exciting growth and development of this field. It is quite clear, however, that despite many general advances an understanding of the precise underlying mechanisms in B-cell tumor development is not yet defined. Probably, there is no single mechanism for all the various forms of B-cell neo­ plastic development. Many different forms of B-cell neoplasms are known, and these are distinguished by several characteristics: 1) the stage of development attained by the tumor stem cells; 2) mode of growth (slow or fast); 3) association with natural or inductive etiologic agents and 4) specific and consistent mutational mechanisms such as retroviral insertion, chromosomal rearrangement. Those charac­ teristic forms which arise naturally in relatively high frequency or those tumors with hallmark properties which can be induced consistently are the models most frequently studied, e. g. , endemic Burkitt's lymphoma, follicular lymphoma, acute and chronic lymphocytic leukemia and mUltiple myeloma in man; bursal lymphoma in chickens; Abelson virus induced pre B cell lymphomas and plasmacytomas in mice and immunocytomas in rats. Each model system, has special problems and advantages.