Classification and concepts of the genera of coryneform bacteria were described on the basis of the results obtained previously. Coryneform bacteria were divided into seven groups at the generic level by the combination of mode of cell division, principal amino acid in the cell wall, the guanine- cytosine content (GC content) in DNA, and biochemical and physiological characteristics. The concepts of several genera were made clearly and a new genus Curtobacterium was proposed. The scheme for differentiation of the genera of these bacteria was presented, and problems for classification of coryneform bacteria were discussed.