Population decline, also known as depopulation, is a reduction in a human population size. Throughout history, Earth's total human population has continued to grow; however, current projections suggest that this long-term trend of steady population growth may be coming to an end.

In world demographics, the world population is the total number of humans currently living. It was estimated by the United Nations to have exceeded eight billion in mid-November 2022. It took around 300,000 years of human prehistory and history for the human population to reach a billion and only 222 years more to reach 8 billion.