Population projections are a basic tool that demographers use to forecast a future population. They can be produced in the form of a prognosis or as prospects. The first is the most likely future development according to the expectations of the projections’ author(s) and is produced in a single variant. The second type is based more on an “if-then” approach and is calculated in more variants. Usually there are three or four variants, viz. low, medium, high, and constant variants. In practice, the medium variant is most widely used and is taken as the most likely or accurate variant, i.e., as a prognosis.