This article summarizes molecular and genetic features of B-cell non-Hodgkin lymphoma and focuses on diffuse large B-cell lymphoma, Burkitt lymphoma, follicular lymphoma, and mantle cell lymphoma. In each of these entities, hallmark genetic aberrations, cytogenetic characteristics, and alterations of single genes that might be involved in the pathogenesis and molecular evolution of the tumor are described. Recent results from gene-expression profiling studies are incorporated that are relevant for the classification of lymphoma entities, the prediction of their clinical behavior, and the identification of deregulated signal-transduction pathways that might represent potential targets in future therapeutic approaches.