Rheumatoid Arthritis (RA) is an inflammatory disease of the joints characterized by the swelling of multiple joints and tenderness caused by progressive inflammatory synovitis, which leads to serious and debilitating diseases. Atopic dermatitis (AD) is a skin condition that may cause a rash and itching due to inflammation of the skin. Ankylosing Spondylitis (AS) is a form of chronic arthritis causing inflammation in the spine. This can cause pain and stiffness in the back. Psoriatic arthritis (PsA) is a type of arthritis (swelling and stiffness in the joints) that is frequently seen in trial participants who also have the skin condition psoriasis. It is caused by the body's immune system mistakenly attacking healthy joint tissue causing inflammation, joint damage, disability, and a reduced life expectancy. This study will assess the adverse events and change in disease symptoms in Korean participants with RA, AD, AS or PsA. Upadacitinib is a drug approved for the treatment of moderately to severely active rheumatoid arthritis, atopic dermatitis, ankylosing spondylitis or psoriatic arthritis. Korean participants who have been prescribed upadacitinib by their physicians will be enrolled. Approximately, 3600 participants will be enrolled this study, in multiple sites within Korea. Participants will receive Upadacitinib as prescribed by the physician and will be followed for approximately 28 weeks. There will be no additional burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the course of the study at a hospital or clinic and will be asked to provide additional information by questionnaire at each visit.