This document describes the demographic transition model, which explains population changes as countries develop from pre-industrial to industrial societies. It outlines four stages: 1) high birth and death rates with slow population growth; 2) high birth rates declining death rates leading to population growth; 3) birth rates beginning to fall while death rates remain low, continuing population growth; and 4) low birth and death rates resulting in steady population levels. It provides characteristics and examples of countries in each stage.