Classification of the inflammatory rheumatic disorders is challenging. They represent a heterogeneous group of conditions, mostly of unknown aetiology. However, a uniform language is essential in facilitating clinical and epidemiological research and, therefore, several different approaches have evolved by which we can classify these diseases. One way in which inflammatory arthropathies are frequently distinguished is by the number of joints affected at presentation. Therefore, this chapter will discuss the differential diagnosis of a monoarthropathy and polyarthropathy. The epidemiology of many of the less common inflammatory disorders is poorly elucidated, but the current knowledge, together with its strengths and weaknesses, will be discussed. Finally, we will describe the overall burden of the musculoskeletal disorders in the community, and then highlight the role of the rheumatologist in the management of these disabling conditions.