This registry will assess the incidence and rate of Humira (monotherapy or combination therapy with MTX) or MTX observational and treatment-emergent SAEs, Adverse Events of Special Interest (AESI) and Pregnancy in patients diagnosed with moderately to severely active polyarticular or polyarticular-course JIA through Year 5. From Year 6 through Year 10 SAEs, a subset of AESI that includes congestive heart failure (CHF), malignancies, AEs at least possibly related to and/or leading to discontinuation of registry treatment and pregnancies will be collected. For JIA patients 2 to< 4 years of age in countries with available local approval for this group of patients at the time of consent to the registry, emergent AESI, SAEs and pregnancy (at the age when a patient can become pregnant) will be collected for the full 10 years. The approved age range for HUMIRA in the U.S., European Union (EU) and in Australia is 4 years of age and older, and recent approval in EU for JIA patients 2 to < 4 years of age.