Epidemiological studies of occlusion and malocclusion not only help in orthodontic treatment planning and evaluation of dental health services but also offer a valid research tool for ascertaining the operation of distinct environmental and genetic factors in the aetiology of malocclusion. The objective of this article was to give an overview on occlusion, malocclusion and the various methods on measuring the occlusion. Each index and method of the assessment described was based on the opinion of an individual or a group of individuals. It had been widely agreed that no particular index or method available that are truly inclusive of all occlusal criteria. Therefore, different indices or method had been developed according to different requirements and it may be necessary to use more than one index in order to gather information to suit the objective of the particular study.