Risk assessment offers a variety of methods which comprise different risk concepts to assess population-based or individual risks. A central epidemiological measure of risk is incidence which is used to derive the relative risk as the ratio between the incidence among subjects exposed and the incidence among subjects unexposed to a certain risk factor. The excess risk quantifies the risk of an exposed population that exceeds the background risk of a non-exposed population. In environmental epidemiology the latter is frequently based on a constant exposure dose over a certain period and is expressed as unit risk. Since the application of different risk concepts depends on the respective study type, we first discuss the different epidemiological study designs. Next, methods to derive the different risk concepts are evaluated and the corresponding statistical measures are presented. Finally, an example illustrates the application of the discussed concepts for individual risk assessment.