Enteric redmouth disease (ERM) is caused by the bacterium Yersinia ruckeri, and is an economically important disease, principally affecting farmed rainbow trout. Since its first description in the Hagerman Valley, Idaho, USA in the 1950s, the causal agent has been shown to be increasingly widespread in a variety of salmonid species in North America. More recently, the disease has been reported, and the bacterium isolated, in many countries and fish hosts throughout the world. Although there has been much work published on this problem, many unanswered questions remain concerning the taxonomy, serological characteristics, epidemiology, and pathogenicity. In particular, we suggest that the development of agreed standard methodologies are needed to make further progress. Despite these limitations, considerable success has been achieved in control of the disease. In this article, we provide a detailed review of the development of immunization for ERM, and the current status of chemotherapy. Overall, we aim to give a comprehensive survey of the many published studies on Y. ruckeri and ERM, in which we bring together the work carried out by various authors.