Purpose: To present the different definitions of peri-implantitis proposed in the literature and to propose a new evidence-based etiology-driven classification of peri-implantitis to accurately and fully describe the etiology of peri-implantitis. Materials and Methods: Full-text papers on the selected topic were obtained for all abstracts and titles that appeared to meet the inclusion criteria. Additional papers were included from the reference lists of the selected studies. No methodologic and reporting quality of the included papers was applied in order to collect the greatest number of articles. Results: One hundred twenty-two studies were found according to the search criteria. After filter activation, abstract evaluation, and duplicate removal, 16 articles were deemed useful for the aim of the present narrative review. A manual search using personal contact and references of published works and contributions by the authors included another 16 articles, resulting in a total of 32 articles. After full-text article selection and reading, 15 articles were finally included. Conclusion: There is not a generally accepted classification system of the various degrees of peri-implantitis. An etiology-driven classification was proposed as a tool to assist the clinician in properly detecting and classifying etiology-based peri-implantitis. This classification may also support the assignment of prognosis, and if needed, therapy to arrest/prevent peri-implantitis. Keywords: classification, dental implants, peri-implant diseases, peri-implantitis