Teeth have been moved in man for centuries and the process of tooth eruption has occurred presumably since he evolved. The cellular and molecular mechanisms which are involved in these two phenomena are amongst the most intriguing questions in dental research today. The aim of this paper is to review some of the theories which have been proposed to explain the two processes. It is also intended to place in context the contribution being made by biological sciences, which might explain tooth eruption and tooth movement. It is not the intention to describe morphologic observations which are well documented and illustrated in more elaborate texts.