Benign breast diseases constitute a heterogeneous group of lesions. In this book, common benign lesions are summarized and their relationship to developing subsequent breast cancer is emphasized. The majority of lesions occurring in the breast are benign. As we know, the most common breast malignancy is in women; however, benign lesions of the breast are far more frequent than malignant ones. The majority of the information that we have available in the literature about the nonmalignant breast diseases is fragmented in texts and innumerable articles. The information provided in this book throughout its fourteen chapters is very complete with regard to the diagnosis of and indications for the treatment of these diseases. Over the last decade, there have been dramatic advances in the imaging techniques employed for the detection and diagnosis of breast cancer, which now include conventional or antilog mastography; digital ultrasound mammography, and magnetic resonance. The most frequent pathologies of the breast, as observed by those of us devoted to Oncology, are of the benign type. However, this is not so for non-specialist physicians and for the women who suffer from these and for whom they are a true cause for alarm. Therefore, it is very important for physicians who are not specialists in cancer to know the signs and symptoms of each of these benign breast diseases in order for them to be able to emit a diagnostic impression and to suggest treatment. Groups of medical specialists with experience in benign diseases of the breast from different institutions in Mexico have been invited to describe the differential diagnosis of benign breast lesions versus breast cancer.