Appropriate selection of therapy for patients with non-Hodgkin lymphoma requires an understanding of the various histologic classifications as well as knowledge of the role of clinical and pathologic staging. The histologic classification of the malignant lymphomas proposed by Rappaport is reviewed. The Ann Arbor Staging System is outlined and its application to NHLs analyzed. Recommendations for clinical staging procedures together with the accuracy of diagnostic tests in the NHL are discussed briefly.