This entry focuses on the number of births per woman in a population. The most commonly used metric is the Total Fertility Rate (TFR) or often simply ‘fertility rate’ – which measures the average number of children per woman.The global average fertility rate is just below 2.5 children per woman today. Over the last 50 years the global fertility rate has halved. And over the course of the modernization of societies the number of children per woman decreases very substantially. In the pre-modern era fertility rates of 4.5 to 7 children per woman were common. At that time the very high mortality at a young age kept population growth low. As health improves and the mortality in the population decreases we typically saw accelerated population growth. This rapid population growth then comes to an end as the fertility rate declines and approaches 2 children per woman.