Caries is a multi-factorial disease, primarily caused by acids. Acids are produced by bacteria which ferment sugar. The aetiology and progress of caries are influenced by life-style and environmental factors, as well as congenital components. Based on, among other things, research concerning twins, the literature suggests that there are hereditary components of caries and life-style and environmental components. With the unravelling of the human genome, it is more easy to study individual genes in relation to the caries process. Because of its multifactorial nature, one has to realise that there is only a beginning of understanding the caries processes at molecular level.