The pathophysiology of the inflammatory arthritides (IA) is complex and the result of interactions between genetic and environmental factors, leading to -in the case of seropositive rheumatoid arthritis-a breach of immune tolerance and subsequent development of joint and systemic manifestations. Regardless of the exact site of the initial immune dysregulation, the synovial membrane is the main target of IA. The heterogeneity of the clinical phenotypes is even more evident on the histological level (pathotypes), which in turn renders research on disease mechanisms more complicated. This article focusses on the various pathotypes of IA.