There are two major differences in concept between this volume and others in the International Histological Classification of Tu­ mours series. The first of these is the inclusion of more clinical aspects than has usually been the case and the second is a con­ centration on a more limited range of conditions. There are sev­ eral reasons for adopting this approach. With regard to both cancer and pre cancer of the oral mucosa, we believe it is impor­ tant that general pathologists, in whose interests this volume has primarily been written, should be informed of the significance of the clinical features of the various lesions under discussion as they may on the whole be unfamiliar with them. Also, we con­ sider it necessary to draw attention to those conditions particu­ lar to the oral tissues that may give rise to appearances which are important in differential diagnosis but can be misleading to the pathologist who does not have detailed knowledge of these tissues. On the other hand, many of the benign and malignant tumours that affect the oral tissues have been dealt with in other volumes in the series and we believe that little or no advantage would be gained by repeating them here.