Decades of epidemiologic research into open-angle glaucoma have elucidated several risk factors related in some way to the disease. As more and more risk factors are identified, however, assessing their individual and collective contributions in a particular patient is becoming increasingly complicated. To help organize our knowledge of risk in glaucoma we first review some concepts of risk and then propose a scheme that places known risk factors into categories (state of the individual, ocular anatomy and physiology, signs of disease, non-glaucoma medications, and personal behaviors) and also indicates how each factor interacts with disease (incidence, prevalence, progression, therapy.) We also describe methods for using risk factors in clinical practice and describe ways that a large and complex body of knowledge can be applied to individual patients.