Lymphoma is the fifth most common type of cancer in the United States, with 74,490 new cases estimated in 2009. Approximately 15% of patients with lymphoma have Hodgkin lymphoma; the remainder have one of the non-Hodgkin lymphomas. The incidence of non-Hodgkin lymphoma has increased steadily over recent decades. This chapter reviews the epidemiology, classification, clinical features, pathology, diagnostic evaluation, staging and prognosis, and treatment of Hodgkin and non-Hodgkin lymphoma. Other topics discussed include the acute and chronic effects of therapy for Hodgkin disease, as well as the subtypes of non-Hodgkin lymphomas, including indolent B cell lymphoma, follicular lymphoma, small lymphocytic lymphoma, mantle cell lymphoma, marginal-zone lymphoma, diffuse large B cell lymphoma (DLBCL), primary central nervous system lymphoma (PCNSL), Burkitt lymphoma, and HIV-related non-Hodgkin lymphoma. Figures illustrate the cellular appearance of Hodgkin lymphoma subtypes and DLBCL, diagnosis of DLBCL subtypes by gene expression, computed tomography and plain chest film in primary mediastinal cell lymphoma, MRI of the brain in PCNSL, and gene expression and gene expression predictors of survival among patients with DLBCL treated with rituximab, cyclophosphamide, hydroxydaunorubicin, vincristine [Oncovin], and prednisone (R-CHOP). Tables describe the Ann Arbor classification and the Cotswold modification for staging of lymphoma; the International Prognostic Score for advanced Hodgkin lymphoma; the World Health Organization classification of hematopoietic neoplasms; chromosomal translocations in non-Hodgkin lymphoma; the Eastern Cooperative Oncology Group performance scale; the International Prognostic Index for aggressive non-Hodgkin lymphoma; and the Follicular Lymphoma International Prognostic Index. This chapter has 185 references.