Polyarticular joint pain involves five or more joints and can be inflammatory or noninflammatory. Two of the most common causes of chronic polyarthritis are osteoarthritis, especially in older patients, and rheumatoid arthritis, which affects at least 0.25% of adults worldwide. The initial evaluation should include a detailed history of the patient's symptoms, with a focus on inflammation, location of pain, duration of symptoms, the presence of systemic symptoms, and any exposures to pathogens that could cause arthritis. Redness, warmth, or swelling in a joint is suggestive of synovitis and joint inflammation. A systematic approach to the physical examination that assesses for a pattern of joint involvement and presence of synovitis can help narrow the differential diagnosis. Laboratory tests, joint aspiration, and imaging studies should be used to confirm a suspected diagnosis. Rheumatoid factor and cyclic citrullinated peptide antibody tests are helpful when there is concern for rheumatoid arthritis. Although magnetic resonance imaging is highly sensitive in identifying erosive bony changes and inflammation, conventional radiography remains the standard for the initial imaging evaluation of rheumatoid arthritis. Point-of-care musculoskeletal ultrasonography can also be a useful tool to detect findings that support a diagnosis of inflammatory arthritis.