The natural history of disease is the course a disease takes in individual people from its pathological onset ("inception") until its eventual resolution through complete recovery or death. The inception of a disease is not a firmly defined concept. The natural history of a disease is sometimes said to start at the moment of exposure to causal agents. Knowledge of the natural history of disease ranks alongside causal understanding in importance for disease prevention and control. Natural history of disease is one of the major elements of descriptive epidemiology.