The principle of Revised European-American Lymphoma (REAL)/World Health Organization (WHO) classification of lymphoid malignancies is to integrate histomorphology features, genetic abnormalities, immunophenotypic characteristics and clinical presentation for the diagnosis and classification of lymphoid malignancies. This new classification scheme has fundamentally changed the concept and the classification of lymphoid malignancies. Retrospective studies have verified that the new classification offers much better clinicopathologic correlation and prognostic significance than any previous classification systems. The classification is now the gold standard for classifying lymphoid malignancies. The goal of this review article is to let the hematologists/oncologist, radiation oncologists and pathologists be familiar with the principles and the clinical significance of the new classification.