Marginal zone lymphoma (MZL) of extranodal mucosa-associated lymphoid tissue (MALT lymphoma), nodal MZL, and splenic B-cell MZL share similar morphologic and immunophenotypic features. All are proliferations of small B lymphoid cells that colonize the marginal zone of reactive germinal centers (GC). These cells were previously described as “centrocyte-like” because their nuclei resemble those of small cleaved follicle center B cells, with slightly irregular nuclear contours, condensed chromatin, and inconspicuous nucleoli, but with more abundant pale cytoplasm. Although the different subtypes of MZL share histologic and immunophenotypic features, they have different clinical, cytogenetic, and molecular genetic features.