This chapter discusses the various technologies available for projecting future population trends. Mathematical extrapolation techniques range from simple arithmetic and geometric projections to sophisticated time-series methods. The ratio method assumes the existence of a population projection for some parent region. Land use techniques generally rely on assumptions about the maximum feasible population of an area. The survival rates are calculated by forming the ratio of actual deaths in a state for some historical period to deaths predicted for that state by applying national survival rates to the state's population. Economic-base population projection techniques are based on the assumption that economic variables play a key role in the determination of demographic variables. The US Bureau of the Census state level population projection model is an excellent example of a single region cohort-component model. The cohort-component model is a powerful forecasting tool because it exploits to the fullest the basic demographic accounting relationships.