Periodontal diseases affect the supporting structures of teeth, i.e. the gingiva (gums), periodontal ligament, alveolar bone and Cementum. Periodontal disease is a pathological condition characterized by a bacterial challenge that can instigate a destructive host response leading to periodontal attachment loss, bone loss and ultimately, possible tooth loss. This chapter aims to describe the prevalence and causes of periodontal diseases. Among the direct causes, thin, adherent microbial film on the tooth surfaces, called dental plaque, is the main pathological cause of gingival and periodontal inflammation. Poor oral hygiene, faulty food habits, poor nutrition, presence of metabolic diseases such as diabetes, use of tobacco, etc. are the major contributory factors for periodontal diseases. It is also known that the use of tobacco, especially habitual chewing of tobacco, presence of metabolic diseases such as diabetes, nutritional deficiencies, compromised immune status and increasing age are associated with an increase in periodontal diseases.