This entry has four sections. We first introduce demography, its principal subject matter, its main concepts, and its general perspectives. Next we review and discuss some of the major writings and theories about population and demography. The classic demographic transition theory (DTT) is the most well‐known explanation in demography, and we discuss it in the third section. Demographic developments in many European and Asian countries have not followed the tenets of DTT, leading to the specification of the so‐called second demographic transition theory (SDTT) and the third demographic transition theory (TDTT), which are discussed in the final section.