The malignant lymphomas, including both Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL), represent a diverse group of diseases that arise from a clonal proliferation of lymphocytes. Each of the more than 30 unique types of lymphoma is a disease with a distinct natural history. This biologic heterogeneity gives rise to marked differences among the lymphomas with respect to epidemiology, pathologic characteristics, clinical presentation, and optimal management. This article emphasizes the principles of diagnosis, including appropriate pathologic evaluation and staging considerations, and focuses on the clinical presentation, staging, and optimal management strategies for the most common types of lymphoma.