A shanty town, squatter area or squatter settlement is a settlement of improvised buildings known as shanties or shacks, typically made of materials such as mud and wood. A typical shanty town is squatted and in the beginning lacks adequate infrastructure, including proper sanitation, safe water supply, electricity and street drainage. Over time, shanty towns can develop their infrastructure and even change into middle class neighbourhoods. They can be small informal settlements or they can house millions of people.

Squatting is the action of occupying an abandoned or unoccupied area of land or a building, usually residential, that the squatter does not own, rent or otherwise have lawful permission to use. The United Nations estimated in 2003 that there were one billion slum residents and squatters globally. Squatting occurs worldwide and tends to occur when people find empty buildings or land to occupy for housing. It has a long history, broken down by country below.