This chapter mainly introduces the development and general situation of the theory and method of demography from the classics to the new era. From the perspective of “general demography,” theories and methods are combined for discussion. The commonly used demographic concepts can be divided into narrow and broad senses. The narrow sense of demography only takes the population’s development process and its laws as the research object, that is, the production and reproduction process of the population as the research object. In this sense, demography is a discipline that conducts scientific research on population, mainly its quantity, composition, and development. It is limited to the study of population changes and their constituent factors, and it does not include population studies other than the process of population development. The narrow sense of demography corresponds to “demography” or “demographic analysis” in English (IUSSP 1992). However, in addition to studying the development process and laws of the population itself, demography in a broad sense also conducts a systematic study of the interrelationships and regularities between the population development process and the economy, society, ecological environment, and other development processes. In this sense, demography is the general term for the study of population development, the regularity and quantitative relationship between population and society, economy, and ecological environment and its application. It is a comprehensive social science, including population theory, demographics, and a series of subdisciplines. The broad sense of demography corresponds to “population study” in English (Li 2001).