Abstract
The world's population continues to grow, albeit at a slower pace. The decelerating growth is mainly attributable to fertility declines in a growing number of countries. However, there are substantial variations in the future trends of populations across regions and countries, with sub-Saharan African countries being projected to have most of the increase. Population momentum plays an important role in determining the future population growth in many countries and areas where fertility is in a rapid transition. With declines in fertility, the world's population is unprecedentedly aging, and the numbers of households with smaller sizes are growing. International migration is also on the rise since the beginning of this century. The world's population is also urbanizing due to increased internal rural to urban migration. Nevertheless, there are uncertainties in future population growth, not only because there are uncertainties in the future trends in fertility, mortality, and migration, but also because there are many other factors that could affect these trajectories. International consensus on climate change and ecosystem protections may trigger population control policies, and the ongoing pandemic is likely to have some impact on mortality, migration, or even fertility.