During the past centuries the basic understanding of periodontal disease and the concepts of etiopathogenesis have evolved and substantially changed. The changes in paradigm has always been followed by the conceptual changes in the classification of periodontal disease. The earliest entirely descriptive classifications were based on the clinical signs and symptoms of periodontal disease. These were followed by a classification system based on the classical pathology paradigm established by Orban and Gottlieb. This was replaced by the next classification reflecting the infection/host response paradigm during the late '60s started with the pioneering works by Loe and coworkers. It is because many data indicated that the host response (determined by genetics, immunology and behavioral factors) was at least as important in the clinical manifestation of periodontal destruction than the bacterial biofilm this classification had been also updated. The AAP published its latest official classification system in 1999. Nevertheless this new system is far from perfect and should evolve as soon as enough data are collected by periodontal research to answer many controversy still existing to day.