The branch of pathology which deals with the research and diagnosis of disease by studying the molecules inside organ, tissues and bodily fluids is termed as molecular pathology. It is generally used to diagnose infectious diseases and cancer. Breast cancer is a type of cancer in which the breast cells grow abnormally. Such cancerous cells divide faster than healthy cells. Breast cancer mostly develops in cells from the lining of milk ducts and the lobules which supply milk to these ducts. The progression of breast cancer from the perspective of molecular pathology views it as a linear process with different steps. It begins as flat epithelial atypia (FEA), progresses to atypical ductal hyperplasia (ADH), transforms into DCIS and finally results in the potentially lethal stage of invasive ductal carcinoma. This book attempts to understand the molecular pathology of breast cancer. It is an upcoming area of research that has undergone rapid development over the past few decades. Those with an interest in this field would find this book helpful.