The use of dental implants has revolutionized the treatment of partially and fully edentulous patients today. Implants have become a treatment approach for managing a broad range of clinical dilemmas due to their high level of predictability and their ability to be used for a wide variety of treatment options. While in many cases dental implants have been reported to achieve long-term success, they are not immune from complications associated with improper treatment planning, surgical and prosthetic execution, material failure, and maintenance. Included in the latter are the biologic complications of peri-implant mucositis and peri-implantitis, inflammatory conditions in the soft and hard tissues at dental implants. It is the purpose of this paper to review the current knowledge concerning peri-implant mucositis and peri-implantitis to aid clinicians in their diagnoses and prevention. It is recognized that new information will continue to emerge, and as such, this document represents a dynamic endeavor that will evolve and require further expansion and reevaluation.