In depth study of the theory of demographic transition. Populations grow exponentially, can quadruple in 100 years, then suddenly stop growing. Why? Demographic transition is a theory which attempts to answer that question. It is based on observation of the history of developed countries. The 4 stages of the theory are examined from a graph of the population growth, the birth rate, and the death rate. Factors which contribute to the birth and death rate are considered, and their effect on the population growth rate.