Purpose To update evidence-based guideline recommendations for practicing oncologists and others on systemic therapy for patients with human epidermal growth factor receptor 2 (HER2)-positive advanced breast cancer to 2018. Methods An Expert Panel conducted a targeted systematic literature review (for both systemic treatment and CNS metastases) and identified 622 articles. Outcomes of interest included overall survival, progression-free survival, and adverse events. Results Of the 622 publications identified and reviewed, no additional evidence was identified that would warrant a change to the 2014 recommendations. Recommendations HER2-targeted therapy is recommended for patients with HER2-positive advanced breast cancer, except for those with clinical congestive heart failure or significantly compromised left ventricular ejection fraction, who should be evaluated on a case-by-case basis. Trastuzumab, pertuzumab, and taxane for first-line treatment and trastuzumab emtansine for second-line treatment are recommended. In the third-line setting, clinicians should offer other HER2-targeted therapy combinations or trastuzumab emtansine (if not previously administered) and may offer pertuzumab if the patient has not previously received it. Optimal duration of chemotherapy is at least 4 to 6 months or until maximum response, depending on toxicity and in the absence of progression. HER2-targeted therapy can continue until time of progression or unacceptable toxicities. For patients with HER2-positive and estrogen receptor-positive/progesterone receptor-positive breast cancer, clinicians may recommend either standard first-line therapy or, for selected patients, endocrine therapy plus HER2-targeted therapy or endocrine therapy alone. Additional information is available at www.asco.org/breast-cancer-guidelines .