Reactive arthritis is classically seen following infection with enteric pathogens such as Yersinia, Salmonella, Campylobacter and Shigella. Inflammatory arthritis has also been described following other enteric infection with organisms such as Clostridium difficile, Brucella and Giardia. Furthermore, arthritis is seen in Whipple's disease, caused by the actinomycete Tropheryma whippelii. This chapter reviews the current understanding of these conditions (with the exception of Brucella, which is discussed in a subsequent chapter). The epidemiology is reviewed, and the contribution of both host and organism to the aetiology and pathogenesis is discussed with particular discussion of the role of HLA-B27 in host susceptibility. Recent work exploring evidence for traffic of pathogenic organisms to the joint is highlighted. A practical approach to the diagnosis and management of the condition is then formulated based, where possible, on clinical trial evidence.