Rheumatoid arthritis (RA) is a chronic inflammatory disease primarily affecting the joints and is associated with significant levels of disability and reduced quality of life. Janus kinase (JAK) inhibitors are a relatively new class of small molecule oral treatments and offer an alternative for patients with RA who do not respond to conventional or biologic therapy. Upadacitinib is a JAK inhibitor engineered to be selective for JAK1, and has recently been approved for use in patients with moderate-to-severe RA. The purpose of this article is to provide a comprehensive review of upadacitinib, including preclinical development and characterization, phase I and II studies, and the phase III SELECT program. Ongoing trials of upadacitinib in additional indications, including spondyloarthritis, inflammatory bowel disease, and atopic dermatitis, are also discussed.