This study aims to evaluate the safety of baricitinib among (A) rheumatoid arthritis (RA) and (B) atopic dermatitis patients treated in routine clinical care. Primary objectives: (1) to compare the incidence rates and profiles of: serious infections overall (including herpes zoster) and opportunistic infections (including tuberculosis, Candida infections, and progressive multifocal leukoencephalopathy), major adverse cardiovascular events, malignancies overall (including lymphoma and typically virus induced malignancies such as cervical and many oropharyngeal cancers), and venous thromboembolism, among patients with long term exposure to baricitinib compared to similar patients with long term exposure to other indicated medications, (2) to describe the incidence rates of the following individual outcomes: lymphoma, herpes zoster, opportunistic infections such as tuberculosis, Candida, and progressive multifocal leukoencephalopathy, rhabdomyolysis, agranulocytosis, hyperlipidaemia (hypercholesterolaemia, hypertriglyceridaemia) - RA only, gastrointestinal perforations, and liver injury. Secondary objectives: (3) to monitor the incidence rates of the aggregate outcomes of serious infections overall, MACE, malignancies overall, and VTE in very elderly patients, that is, those ≥75 years of age, (4) to assess the effectiveness of risk minimisation activities by describing the pattern of use of baricitinib and the occurrence of pregnancy, active tuberculosis or active viral hepatitis, and monitoring and treatment of lipid levels in relation to such use in routine clinical care.