The epidemiologist works with researchers in various disciplines as well as public and private health practitioners who are responsible for maintaining and improving the health of the population. Health is defined as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity”(WHO, 1948). The role of the epidemiologist is to provide information on the extent, etiology and risk of disease or injury. Key to this role is knowledge of the location, size and demographic makeup of the population at risk for developing disease or injury. By integrating this information with the location of cases as well as risk factors, epidemiologists can make a vital contribution to disease and injury prevention, intervention and response. This applies both to endemic or “usual” levels of both chronic diseases like cancer or heart disease and infectious diseases like pneumonia or influenza, and injuries like gunshot wounds or motor vehicle accidents. It also applies to disease epidemics or outbreaks like SARS; attacks by biological or chemical weapons such as Anthrax, ricin or sarin; and inadvertent natural or technological disasters including earthquakes, transportation disasters or widespread power interruptions. This chapter explores the types of census data for disease surveillance, prevention and intervention.