This tenth fascicle of the Atlas of Tumor Pathology focuses on the morphology of breast legions. This volume is composed of 18 chapters, an appendix, and contents sections. It contains 474 figures, some of which include more than one image. All illustrations in this 418-page book are in full color. Ductal proliferative lesions and in situ ductal carcinomas are evaluated according to Dr. Tavassoli's ductal intraepithelial neoplasia (DIN) terminology. A chapter on DIN provides an update of Dr. Tavassoli's current approach and, moreover, gives the reader a chance to understand the proposed differences compared to WHO classification. Breast carcinomas are discussed in three categories: major types, low-grade carcinomas, and rare carcinomas. The definitions of tumor types; alternative terminologies; macroscopic, micrscopic, and cytologic findings are comprehensively detailed. This Atlas will serve as a guide to both general and breast pathologists on the way to diagnosis.