Diagnosis of periprosthetic joint infection (PJI) remains challenging as no “gold standard” for diagnosis exists. The challenge is then what test(s) or criterion(ia) can be used to define PJI. In an effort to standardize the definition of PJI, Musculoskeletal Infection Society (MSIS) convened a workgroup in 2011 to issue diagnostic criteria for PJI. The MSIS definition of PJI consists of two major criteria, when the presence of either criterion would indicate PJI, and six minor criteria, when the presence of four or more would indicate PJI.