Targeted therapies against the human epidermal growth factor receptor HER2, have led to revolutionary strides in breast cancer research and treatment. Clinical therapeutic decisions in the treatment of patients with HER2 positive metastatic breast cancer are based on appropriate patient selection, the clinical situation, and data related to the available therapeutic agents trastuzumab and lapatinib. Trastuzumab was the first agent tested and approved in 1996 as single agent for patients with chemotherapy-refractory disease, and in combination with paclitaxel as first-line treatment. This intravenous humanized monoclonal antibody is directed against the extracellular domain of the HER2 protein. Lapatinib, an oral small molecule tyrosine kinase inhibitor has more recently become available (in 2007), approved for used in combination with capecitabine for patients with HER2 positive metastatic disease that has progressed on trastuzumab. Important questions and controversies still remain and are reviewed, including patient selection for anti-HER2 treatment of metastatic disease based on HER2 testing, dose scheduling of trastuzumab, duration of therapy, tolerability, role of lapatinib and clinical significance of trastuzumab resistance and efficacy. Ongoing trials designed to maximize the therapeutic ratio of these agents, are also discussed.