Risk is the probability that an individual will develop a specific disease in a given period, which may vary from one individual to another. Risk assessment involves identifying elements that either may predispose a patient to developing periodontal disease or may influence progression of disease that already exists. Risk factors are associated with the development and progression of the disease, but are not necessarily causative. This chapter covers the terminologies, risk factors for periodontal disease, risk determinants/background characteristics for periodontal disease, risk indicators for periodontal disease, risk markers/predictors, and clinical risk assessment for periodontal disease. Risk factors may be environmental, behavioral or biologic factor that, when present, increases the likelihood that an individual will develop the disease. Risk markers are associated with increased risk for disease, but do not cause the disease. These factors are also identified in cross-sectional and longitudinal studies. A risk factor that can be used to predict the future course of disease is known as a risk marker.