The UN says the milestone represents improvements in public health, nutrition, personal hygiene and medicine, as well as high and persistent levels of fertility in some countries.
A baby born somewhere on Tuesday will be the world's eight billionth person, according to a projection by the United Nations.
"The milestone is an occasion to celebrate diversity and advancements while considering humanity's shared responsibility for the planet," UN Secretary-General Antonio Guterres said in a statement.
The UN attributes the growth to human development, with people living longer thanks to improvements in public health, nutrition, personal hygiene and medicine.
It is also the result of higher fertility rates, particularly in the world's poorest countries.
How many is too many?
Population growth has also magnified the environmental impacts of economic development.
But while some worry that eight billion humans is too many for planet Earth, most experts say the bigger problem is the overconsumption of resources by the wealthiest people.
"Some express concerns that our world is overpopulated," said United Nations Population Fund chief Natalia Kanem. "I am here to say clearly that the sheer number of human lives is not a cause for fear."
Joel Cohen of Rockefeller University's Laboratory of Populations said the question of how many people Earth can support has two sides: natural limits and human choices.
Our choices result in humans consuming far more biological resources, such as forests and land, than the planet can regenerate each year.
The overconsumption of fossil fuels, for example, leads to more carbon dioxide emissions, responsible for global warming.
The current population is more than three times higher than the 2.5 billion global headcount in 1950.
However, after a peak in the early 1960s, the world's population growth rate has decelerated dramatically, Rachel Snow of the UN Population Fund said.
Annual growth has fallen from a high of 2.1 percent between 1962 and 1965 to below 1 percent in 2020, and could potentially fall further to around 0.5 percent by 2050 due to a continued decline in fertility rates, the United Nations projects.
The UN projects the population to continue growing to about 8.5 billion in 2030, 9.7 billion in 2050, and peaking around 10.4 billion in the 2080s.