Because of progress in immunology, specifically the discovery of the B- and T-lymphocyte systems, it was imperative to rethink the concepts of malignant lymphomas, which resulted in the development of new lymphoma classifications. One of these was the Kiel classification, proposed by the European Lymphoma Club in 1974. During the following years the classification was refined, correlated with clinical findings, discussed at length, and put to the test against other classifications. It was soon widely accepted in Europe and later sparked the founding of the European Association for Haematopathology in Geneva, Switzerland, in 1988. In 2001 the Kiel classification was incorporated into the new WHO classification.