Chronic inflammatory periodontal disease and its related condition, peri‐implant disease, are highly prevalent globally and require accurate and speedy diagnosis. The focus of this volume dedicated to diagnostics is to cover modern enhancements in accuracy, simplicity and speed. An international assortment of experts has been tasked with reviewing defined areas of current best practice as well innovation in the field of periodontitis and peri‐implantitis diagnostics. Periodontitis and peri‐implantitis are irreversible, chronic, cumulative conditions propagated by bacteria and host factors, which involve soft and hard tissue changes, and these changes are measured in the diagnostic process. Clinically relevant modifications to the healthy state are detected using clinical, radiological and laboratory or point of care testing, and these testing approaches are critically reviewed at length in this state‐of‐the‐art resume of periodontal diagnostics.