Peri-implant mucositis has been defined as a reversible inflammatory reaction in the soft tissues around a functioning implant with no bone loss. This paper reviews the prevalence, etiology, risk indicators, prevention, and treatment of mucositis. Relying on the literature concerning mucositis, the bacterial etiology is discussed as well as the varying ranges of prevalence, reported to be from 20% to 80% of subjects (13% to 62% of implants) after a minimum of 5 years of implant function. A discussion of the definition of mucositis questions the assumption of it being completely reversible following treatment and challenges the concept of mucositis "transfer" (conversion) to peri-implantitis.