This is a study evaluating a 28-day course followed by a 56-day course of itacitinib in patients with active rheumatoid arthritis (RA). The study will evaluate safety and efficacy parameters of itacitinib.

Inclusion Criteria:

• Subjects with active RA aged 18 to 75 years of age and meet tender and swollen joint assessment expectations defined in the study protocol.
• c-Reactive protein (CRP) or erythrocyte sedimentation rate (ESR) laboratory values meet minimal study protocol expectations.

Exclusion Criteria:

• Females who are pregnant or breastfeeding.
• Men and women who cannot comply with requirements to avoid fathering a child or becoming pregnant, respectively.
• Subjects treated with a biologic agent within 12 weeks prior to first dose of study drug. (12 months in the case of rituximab.)
• Subjects with a history or currently suspected inflammatory disease other than RA.
• Subjects with a history of hematological disorders.