The World Health Organization (WHO) classification has been developed under the joint auspices of the European Association for Hematopathology (EAHP) and the Society for Hematopathology (SH). First organized in 1995, the Steering Committee appointed 10 committees for T-cell and B-cell lymphomas and leukemias and myeloid and histiocytic tumors to develop a relevant list of diseases and establish definitions of each disease according to established criteria. The WHO classification uses the principles of the Revised European American Classification of Lymphoid Neoplasms (REAL), which defines each disease according to its morphologic features, immunophenotype, genetic features, postulated normal counterpart, and clinical features. The proposed classification was presented at the United States-Canadian Academy of Pathology meeting in 1997. The Steering Committee also appointed a Clinical Advisory Committee to ensure that the classification meets clinical needs and to resolve questions of clinical significance. The proposed WHO classification for lymphomas is similar to the REAL classification for lymphomas, with minor modifications and reassessment of provisional categories based on new data since 1994.