Clostridium difficile is now considered to be one of the most important causes of health care-associated infections. C. difficile infections are also emerging in the community and in animals used for food, and are no longer viewed simply as unpleasant complications that follow antibiotic therapy. Since 2001, the prevalence and severity of C. difficile infection has increased significantly, which has led to increased research interest and the discovery of new virulence factors, and has expanded and focused the development of new treatment and prevention regimens. This Review summarizes the recent epidemiological changes in C. difficile infection, our current knowledge of C. difficile virulence factors and the clinical outcomes of C. difficile infection.