Population growth refers to the increase in the number of people in a population or dispersed group over time. The "population growth rate" is the rate at which the number of individuals in a population increases in a given time period, expressed as a fraction of the initial population. The growth rate can be calculated by subtracting population loss, or the combined rates of mortality and emigration, from population gain, or the combined rates of fertility and immigration.

Factors affecting population growth include fertility, mortality, and migration. Fertility is the number of offspring produced on average by an individual species member under certain environmental conditions over a period of time. Most populations do not grow exponentially, rather they follow a logistic model. Once the population has reached its carrying capacity, it will stabilize and the exponential curve will level off towards the carrying capacity, which is usually when a population has depleted most of its natural resources.

The worlds human population has grown from 1 billion in 1800 to over 8 billion in 2023. The world population growth rate peaked in 1963 at 2.2% per year and subsequently declined. In 2017, the estimated annual growth rate was 1.1% . While the global population is still increasing in absolute numbers, population growth peaked decades ago. The UN expects rates to continue to fall until the end of the century. In fact, towards the end of the century, it projects negative growth, meaning the global population will shrink instead of grow.

Population growth has significant impacts on the Earth system, including increasing ecological impacts on environments, altering interactions among organisms, and the transmission of diseases.