Accumulations of dental plaque adjacent to the gingival margin which result in gingival inflammation have been termed marginal gingivitis. Recently an international consensus report defined gingival disease. The two broad categories were plaque-induced disease and non-plaque-induced disease. The hallmark of plaque induced disease is a stable periodontal attachment. Nonetheless, the clarification of the various types of plaque-induced gingival diseases recognized clinically, did little to differentiate their etiology, other than the requirement for supragingival plaque. Thus, the differences which have been observed between so-called 'experimental' and 'chronic' gingival disease were not apparent. However, the better understanding of the microbial ecology of marginal supragingival dental plaque will provide a better understanding of the etiology of these diseases. The advances in bacterial identification and other methodologies may help delineate the differences among these diseases microbiologically.