The understanding of diagnostic lymph node and spleen pathology has evolved at an impressive pace since 1995, when the third series AFIP atlas was published. Progress has been fuelled, in large part, by the application of a number of technologies to the study of hematopoietic neoplasms. The World Health Organization (WHO) classification scheme for hematologic neoplasms has captured much of this progress, and is generally accepted for clinical practice. The current volume, part of the fourth series of atlases, integrates the WHO classification, including the 2016 revision, and highlights areas in which the WHO classification is likely to evolve with time. In keeping with the goals and tradition of the atlases, this volume emphasizes morphological features of hematopoietic neoplasms, and includes a discussion of differential diagnoses for each disease category. In addition, the results of immunophenotypic and molecular genetic testing for each disease are highlighted, including findings generated by using high-throughput techniques that likely will be integrated into standard diagnostics in the near future. Overall, this atlas will provide readers with the comprehensive information necessary for the pathological and clinical assessment of lymph node and splenic lesions.