Extreme poverty is the most severe type of poverty, defined by the United Nations (UN) as "a condition characterized by severe deprivation of basic human needs, including food, safe drinking water, sanitation facilities, health, shelter, education and information. It depends not only on income but also on access to services". Historically, other definitions have been proposed within the United Nations.

Extreme poverty mainly refers to an income below the international poverty line of $1.90 per day in 2018 ($2.66 in 2024 dollars), set by the World Bank. This is the equivalent of $1.00 a day in 1996 US prices, hence the widely used expression "living on less than a dollar a day". The vast majority of those in extreme poverty reside in South Asia and Sub-Saharan Africa. As of 2018, it is estimated that the country with the most people living in extreme poverty is Nigeria, at 86 million.

In the past, the vast majority of the world population lived in conditions of extreme poverty. The percentage of the global population living in absolute poverty fell from over 80% in 1800 to around 10% by 2015. According to UN estimates, in 2015^[update] roughly 734 million people or 10% remained under those conditions. The number had previously been measured as 1.9 billion in 1990, and 1.2 billion in 2008. Despite the significant number of individuals still below the international poverty line, these figures represent significant progress for the international community, as they reflect a decrease of more than one billion people over 15 years.

In public opinion surveys around the globe, people surveyed tend to think that extreme poverty has not decreased.

The reduction of extreme poverty and hunger was the first Millennium Development Goal (MDG1), as set by the United Nations in 2000. Specifically, the target was to reduce the extreme poverty rate by half by 2015, a goal that was met five years ahead of schedule. In the Sustainable Development Goals, which succeeded the MDGs, the goal is to end extreme poverty in all its forms everywhere. With this declaration the international community, including the UN and the World Bank have adopted the target of ending extreme poverty by 2030.

In July 1993, Leandro Despouy, the then UN Special Raporters on extreme poverty and human rights made use of a definition he adapted from a 1987 report to the French Economic and Social Council by Fr. Joseph Wresinski, founder of the International Movement ATD Fourth World, distinguishing "lack of basic security" (poverty) and "chronic poverty" (extreme poverty), linking the eradication of extreme poverty by allowing people currently experiencing it a real opportunity to exercise all their human rights:

The lack of basic security connotes the absence of one or more factors enabling individuals and families to assume basic responsibilities and to enjoy fundamental rights. The situation may become widespread and result in more serious and permanent consequences. The lack of basic security leads to chronic poverty when it simultaneously affects several aspects of people's lives, when it is prolonged and when it severely compromises people's chances of regaining their rights and of reassuming their responsibilities in the foreseeable future.

This definition was mentioned previously, in June 1989, in the preliminary report on the realization of economic, social and cultural rights by the UN Special Rapporteur Danilo Türk. It is still in use today, among others, in the current UN Guiding Principles on Extreme Poverty and Human Rights adopted by the UN Human Rights Council in September 2012.