Extranodal marginal zone B-cell lymphomas of the MALT type constitute, with around 8% of all B-cell lymphomas, the third most frequent lymphoma in the Western hemisphere. Their unifying characteristic principle is their origin in organs that are typically devoid of a regular lymphatic parenchyma ("primary" MALT). In contrast, "secondary" MALT is acquired in these sites by chronic inflammatory processes triggered by chronic infections or autoimmune diseases. The organotypic characteristics of these particular lymphoid tumours are also mirrored by organ-specific precursor lesions and in tumour biology. Usually, MALT-type lymphomas remain confined to their site of origin for a long time, disseminating only late during the course of the disease. Hence, they may be controlled by local treatment (excision, irradiation). Moreover, the distinctive genetic constitution of MALT-type lymphomas, although varying from organ to organ, indicates particular transformation pathways obviously related to the specific precursor lesion and, hence, of organ-specific quality.