Within the past decade, the discipline of adolescent and young adult (AYA) oncology has taken root in the United States. It arose from the observation that survival improvements for 15-39-year-olds have lagged behind those of both children and older adults. Rapid progress in this new area has resulted from energetic work by researchers, clinicians, and non-profit organizations focusing on AYA-aged cancer patients and survivors. The term "AYA" is now well recognized within both pediatric and medical oncology, and AYA-specific aims are increasingly included in clinical trials and also basic and translational oncology research. The AYA oncology movement in the United States was spearheaded by the LIVESTRONG Young Adult Alliance (the Alliance), a coalition of AYA-focused non-profit organizations and academic institutions that has recently transitioned into a successor organization-Critical Mass: The Young Adult Cancer Alliance, composed of individual AYAO professionals. The work of groups such as the Alliance/Critical Mass and key collaborators-including the National Cancer Institute, National Comprehensive Cancer Network, Children's Oncology Group, and advocacy organizations-provides a useful platform for the discussion of progress in AYA oncology in the United States, including advances in (1) research and tool development; (2) public and professional education; (3) advocacy and patient support; (4) awareness; and (5) service delivery. AYA oncology programs are now burgeoning dramatically throughout the United States, and many well-established U.S. programs share distinctive features in clinical programming. The United States is now entering an era of larger-scale coordinated efforts in research, advocacy, and clinical care for AYAs with cancer.