Abemaciclib (Verzenio™) is an orally administered inhibitor of cyclin-dependent kinases 4 and 6 that is being developed by Eli Lilly and Company. Abemaciclib has been approved in the USA for the treatment of hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced or metastatic breast cancer, in combination with fulvestrant in women with disease progression following endocrine therapy, and as monotherapy in adult patients with disease progression following endocrine therapy and prior chemotherapy in the metastatic setting. In addition, abemaciclib is in various stages of development internationally for a variety of cancers. This article summarizes the milestones in the development of abemaciclib leading to its first approval for the treatment of patients with HR-positive, HER2-negative advanced or metastatic breast cancer.