Due to the topology and structure of the lymph nodes, their role in the pathogenesis and development of diseases is a very special one. Each organ and even each organ-related region of the body has its own group of lymph nodes, specific topological reactions, such as in circumscribed inflammation or in the metastatic spread of malignant tumors. On the other hand, all the lymph nodes of an organism join in a uniform function effected by highly differentiated structures. Volume 84 of Current Topics in Pathology presents our current knowledge about the structure and reaction patterns of this "sec ondary" lymphoid organ. Despite our original intention to publish all the contributions in one book, it became necessary to divide them: Part 1 focuses on the involved nodal compartments, cell types, and functions, while Part 2 describes their reactions in inflammatory, neo plastic, and immune-deficient diseases. Even with the cooperation of more than 30 authors, the coverage cannot be exhaustive. The scope of both parts is limited to those reactions that can be described by direct and indirect morphological methods, including modern tech niques such as immune electron microscopy.