Increasing geographical range and the ability of alphaviruses to cause major disease outbreaks highlight their growing importance in clinical practice. Alphaviruses are now the most common cause of infectious arthritis worldwide. A significant number of symptomatic infections result in arthralgia that can incapacitate for weeks. Acute manifestations are often severe and highly debilitating, affecting multiple joints. Furthermore, rheumatic symptoms may persist for months. Chronic arthritis has also been described; however, symptoms beyond 3-6 months can usually be attributed to an alternative disease. Fatigue and malaise often accompany the infection-related arthritis, causing high morbidity, which has an important economic impact. In this chapter, the clinical manifestations associated with some of the more important arthritogenic alphaviruses are described.