Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death in women worldwide, accounting for nearly a quarter of the total new cancer cases each year. Of these cases, approximately 15-25% overexpress HER2, a transmembrane RTK kinase that is associated with aggressive tumor growth and poor outcomes. However, in the past decade, survival rates of patients with HER-positive breast cancer have significantly improved due to increased screening, HER2 testing, and breakthrough HER2-targeted drug therapies. The Handbook of HER2-Targeted Agents in Breast Cancer provides oncologists, primary care physicians, trainees, and other healthcare providers with a concise, accessible, and up-to-date survey of the field, including a review of our current understanding of the biology of the HER2 pathway and the rationale for targeting it in early-stage and advanced breast cancer.