 Peri-implant diseases have been steadily rising in prevalence due to the increased use of dental implants. The World Workshop on the Classification of Periodontal and Peri-implant Diseases, 2017, aim to clarify the existing knowledge on these diseases by providing a comprehensive overview of the current understanding of the disease and its treatments. This article was authored by Antonio Scorano, Amad G.A. Cater, Sergio Alexander-Guerca and others.