Endocrine therapy is recommended for patients with hormone receptor-positive (HR) advanced and metastatic breast cancer without visceral crisis (symptomatic visceral disease). However, many patients experience disease progression during treatment, and most patients eventually develop endocrine resistance. Therefore, it is important to identify treatment options that prolong the effectiveness of first-line endocrine therapies. Ribociclib is an orally bioavailable cyclin-dependent kinase (CDK) 4/6 inhibitor that has been approved for use in combination with an aromatase inhibitor for the treatment of HR, human epidermal growth factor receptor 2-negative (HER2) advanced breast cancer. This approval is based on findings from the MONALEESA-2 study, a double-blind, placebo-controlled, randomized phase 3 trial (NCT01958021) in which first-line therapy with ribociclib + letrozole significantly improved progression-free survival (PFS) compared with placebo + letrozole in patients with HR/HER2 advanced breast cancer. This review will discuss the overall findings from the MONALEESA-2 study and will provide a summarized analysis of results from the available subgroups in the study by age, visceral metastases, bone-only disease, de novo disease, and prior therapy. On the basis of these data, ribociclib has established itself as a beneficial treatment option for these different populations. TRIAL REGISTRATION: ClinicalTrials.gov, NCT01958021 . Registered on 8 October 2013.