Early arthritis is challenging because the clinical picture often does not allow a distinction between rheumatoid arthritis (RA), self-limiting disease, and other forms of inflammatory arthritis. In Germany the first early synovitis clinic and several inception cohorts of patients with early RA were initiated and evaluated during the 1980s and 1990s to learn more about diagnostic classification, psycho-social problems and socio-economical status including sick-leave, work loss, and indirect costs of patients with early arthritis and early RA. Unclassified arthritis was described as the most frequent diagnosis and the term "undifferentiated arthritis" was chosen to underline the heterogeneity of theses arthritides and the preliminary state of this classification as a working diagnosis. A large National Databank of the German Regional Collaborative Arthritis Centres has been established over the last 10 years. In total, there are some 170,000 cases in the database. Moreover, a prospective multicentre inception cohort of early RA of less than 1 year's disease duration has been started recently to evaluate parameters of potential relevance for the pathogenesis of RA and eventually for the prediction of erosive disease. Studies are in progress to test the diagnostic performance of specific antibodies and antibody patterns for RA. Another topic of research addresses the identification of bacterial DNA in synovial fluid and synovial tissues to improve the differentiation of patients with reactive arthritis from those with early RA and to narrow the working diagnosis of undifferentiated arthritis.