In the introduction to Chapter 1 it was stressed that in order to decide whether a disease is a public health problem it is important to be able to answer some key questions about it. Is the disease widespread? Is it on the increase? What individuals or groups appear to be susceptible? Do we know what causes it? Can it be prevented? What is the impact of the disease on the individual and society? The epidemiology of oral diseases can provide some detailed answers to these important questions. This chapter will present a brief overview of trends in oral diseases for children and adults in the UK. It will focus on periodontal disease, oral cancer, and dental caries, but there is also a brief section on dental trauma and erosion. Dentofacial anomalies, per se, are not diseases but will be included here, as their prevalence and incidence have implications for dental care because of the impact on social and psychological well-being. The impact on health will be presented. The problems of oral health inequality will be reviewed and the implications of trends in oral diseases for dental care in the UK will be discussed. There are many surveys describing the oral health of children and adults in the UK, with decennial national surveys of both groups since 1973. Scotland has not participated in the two most recent surveys, children in 2003 and adults in 2009. In these surveys all dental examiners are trained and calibrated, so that the diagnostic criteria are consistent and national trends can be identified. See Chapter 5 for a brief description of the importance of standardization of diagnostic criteria. In addition, the British Association for the Study of Community Dentistry (BASCD) undertakes surveys of the oral health of children within the districts of the UK; again, examiners are trained and calibrated and changes in trends in oral health across smaller areas can be monitored at shorter intervals than in the 10-yearly national surveys. Details of these surveys, including diagnostic criteria, can be found at http://www.bascd.org/oral-health-surveys. Current concepts in relation to periodontal disease have changed considerably in the last 20–30 years. The traditional ‘progressive’ disease model has been replaced by the ‘burst theory’. That is, periodontal diseases have short ‘bursts’ of activity followed by long periods of remission and healing (Goodson et al. 1982; Socransky et al . 1984).