This document provides information about population explosion and related topics. It discusses environmental factors affecting human settlement, defines population and overpopulation. Some key reasons for overpopulation mentioned are increased birth rate and decreased death rate due to better medical facilities. Food production and the world's food problem are also covered. Theories around population growth such as the demographic transition theory, Malthusian theory of maximum population, and optimum population theory are summarized. Population dynamics and exponential growth models are briefly explained with equations. A case study on Dharavi slum in Mumbai is also included.