This essay is the first chapter in a larger project aimed at updating my knowledge, analysis and views on global population dynamics. This paper provides a quick, yet comprehensive, overview of the demographic transition; who came up with the theory and how it has evolved over time. The first edition of this chapter was published in April 2021, but it was updated in January 2022 with reference to Devanthal et al. (2021). In September 2022, a new version was uploaded with a single-column design.