The aim of this atlas is to illustrate the wide range of histological appearances which can be seen in brea. st biopsies and mastectomy specimens. An attempt has been made to include photomicrographs showing the more usual appearances as well as some of the unusual patterns encountered in most common lesions of the breast. In addition some of the rarer forms of mammary pathology have been illustrated, sometimes extensively, where this was considered important in the differential diagnosis and where photomicrographs of good quality were available. Some of the low power photomicro- graphs lack detail but have been retained as they illustrate Important microanatomical or architectural patterns. The majority of the photomicrographs are of histological preparations stained with haematoxylin and eosin, buta few special stains have been used to illustrate certain specific features. Only occasional photographs of gross specimens have been included. This is notto belittle the importance of gross appearances: indeed micro- scopic examination of any tissue should always be complemented by careful naked-eye examination.A few mammographic pictures have also been included to illustrate characteristic patterns. There are no photo- micrographs of cytological preparations as these were considered outside the scope of this book and excellent atlases of mammary cytology already exist. It is hoped thatthisatlaswill prove useful to surgical pathologists and others interested in the histological appearances of the breast. It is not intended as a comprehensive study of breast diseases, and details of clinical presentation and treatment have only been mentioned briefly.