For some time, it has been clear that a global population imbalance is emerging. High income countries, including nearly all of the Americas, Europe, and most of East and parts of South and Southeast Asia, have seen a dramatic, sustained fall in fertility. Already, this is resulting in shrinking labor forces and the oldest mean age populations seen in history. At the same time, the low income countries and even some lower middle-income countries—mainly in Africa but also in Central America, the Middle East, and parts of South and Southeast Asia—continue to have relatively high fertility. This is now, and even more in the coming decades, producing fast-growing labor forces and relatively young populations.