This fourth edition presents an updated and expanded text and illustrations to reflect continued morphologic, immunophenotypic, and especially molecular advances in the field of neoplastic hematology, mostly due to the rapidly expanding application of next-generation sequencing. Those advances not only allow a more reliable diagnosis of the majority of tumors and identification of early changes such as monoclonal B-cell lymphocytosis or clonal hematopoiesis of indeterminate potential (CHIP), but also in many cases identify mutations or phenotypic changes in tumors that can be targeted by mutation-specific or antigen-specific drugs. This edition incorporates the updated WHO classification of hematopoietic tumors and new immunophenotypic and molecular markers to provide a thorough pathologic overview of hematologic neoplasms while focusing on flow cytometric features. Special emphasis has been put on hematological neoplasms with crucial clinical significance such as acute promyelocytic leukemia, other acute leukemias, and difficult areas in flow cytometry. Flow cytometric features in AML, MDS, CMML, CLL and measurable residual disease were significantly expanded. There are many new comparative tables, illustrations, and diagrams of algorithmic approaches.