This essay describes the relationship of population to the overall development process and is based on a special university lecture given at the London School of Hygiene in February, 1974. The contents include discussions of population trends, reasons for the population explosion, the structure of populations, development inequalities, urbanization, education, employment, health needs, and family planning programs. There is a list of references at the end of the essay. International Planned Parenthood Federation publications for further reading are also given. (Author/MA)