Baricitinib (Olumiant®) is an oral, targeted synthetic DMARD that inhibits JAK1 and JAK2, which are implicated in the pathogenesis of rheumatoid arthritis (RA). This novel, small molecule is approved for use as monotherapy, or in combination with methotrexate, for the treatment of adults with moderate to severe active RA who responded inadequately to or were intolerant of ≥ 1 DMARD. In pivotal multinational trials, once-daily baricitinib 4 mg, with/without methotrexate (± another csDMARD), improved the signs and symptoms of RA, disease activity and physical function in DMARD-naive patients and in patients with an inadequate response to methotrexate, csDMARDs or TNF inhibitors; baricitinib treatment also slowed structural joint damage in DMARD-naive patients and in those with an inadequate response to methotrexate and csDMARDs. Baricitinib plus methotrexate was more effective than adalimumab plus methotrexate in patients with an inadequate response to methotrexate. The onset of these benefits was generally rapid and sustained over time. Baricitinib was generally well tolerated during up to 5.5 years' treatment; the most commonly reported adverse drug reactions were upper respiratory tract infections, increased LDL cholesterol, nausea and thrombocytosis. Thus, once-daily baricitinib, as monotherapy or in combination with methotrexate, is an effective and generally well tolerated emerging treatment for patients with moderate to severe active RA who have responded inadequately to or are intolerant of ≥ 1 DMARD, and extends the options available for this population.