Pertuzumab, a humanized monoclonal antibody and the first in the class of agents called the HER2 dimerization inhibitors, impairs the ability of HER2 to bind to other members of the HER family. It has a unique and complimentary mechanism of action compared with trastuzumab, and the combination has resulted in the enhanced blockade of the HER signaling pathway. When pertuzumab was used in combination with docetaxel and trastuzumab in the first-line treatment of metastatic HER2+ breast cancer, it led to an overall survival benefit. Pertuzumab has therefore been approved by the FDA and is currently used as a standard of care for this indication. It is also the first agent in oncology to receive accelerated FDA approval in the neoadjuvant setting. Randomized trials showed that the addition of pertuzumab to trastuzumab based chemotherapy improves pathologic complete response rates in HER2+ early-stage breast cancer. A randomized phase III clinical trial with disease-free survival as the primary end point is evaluating the safety and efficacy of pertuzumab in the adjuvant setting. This article describes the preclinical data, synthesizes available data from phase I–III clinical trials of pertuzumab in early stage and metastatic settings, and puts them into perspective with current treatment recommendations and future research developments.