Periodontal Diseases are almost universally considered to be the result of the microbial infection leading to a host inflammatory response. The diagnoses of periodontal diseases are also not as straight forward as one might imagine, it requires research and development of original diagnostic tools that will expectantly demonstrate ever increasing sensitivity and specificity. It should be recognized that none of these parameters are intended to determine etiology of periodontal disease. Therefore a useful new diagnostic technology either provides information more efficiently than existing technologies or it provides valuable information that cannot be provided by existing technologies. An attempt is made to review the literature on clinical and microbiological diagnosis in periodontal diseases.