Much has been learned in the past decade from the study of tissues involved by the disorder long known as Hodgkin's disease. Two important discoveries have prompted changes in classification and nomenclature: first, the recognition that there are two distinct lymphomas encompassed within this category (classical and nodular lymphocyte-predominant [NLP] types), and second, the discovery that the Reed-Sternberg (RS) cells in most cases are monoclonal B cells. Thus "Hodgkin's disease" comprises two distinct lymphomas, deserving of a name change, to "Hodgkin's lymphomas" (HLs). The immunophenotype and genetic features of both classical HL and NLPHL have been defined. These are useful in the subclassification of HL and in distinguishing HL from two recently described, aggressive lymphomas that were in the past often diagnosed as HL: anaplastic large-cell lymphoma, T-cell type (ALCL), and T-cell/histiocyte-rich large B-cell lymphoma (T/HRBCL). Despite the advances of recent years, many questions remain to be answered, and these will provide the challenges of the next decade.