The indolent B-cell non-Hodgkin's lymphomas are a diverse group of disorders that differ markedly with respect to presenting features and natural history. This article reviews entities that have generally been encompassed under the category of indolent lymphomas in various classifications, including the Working Formulation, although many were not specifically identified or labeled as separate entities. These include small-lymphocytic lymphoma (SLL), lymphoplasmacytoid lymphoma, the follicle center cell lymphomas, mantle cell lymphoma, and nodal and extranodal marginal zone lymphomas, including mucosa-associated lymphoid tissue (MALT) lymphoma. There is still a great deal to be learned about the basic biology and treatment of these disorders. Numerous variables influence the type of management used for each individual case, including the disease entity and stage, symptoms and real or threatened organ dysfunction, patient age, and medical condition, as well as the preferences of the patient and practitioner. Unfortunately, because of the inadequacy of current treatment, the majority of patients with indolent lymphoma will not be cured. Thus, continued investigation in the laboratory and through carefully designed clinical trials is essential.