The two most common rat species live in close association with people. Black rats prefer roofs, attics and other high places, while Norway rats are more likely to dwell on the ground. Both species often live on ships, which is how they came to have a global distribution.
The Norway rat was originally a forest-dwelling northern Asian species. Today, it is found worldwide in and near human habitations, especially port cities. They often occupy basements of buildings, while the more acrobatic black rat lives on their roofs. Black rats are native to South Asia and so closely associated with ship infestations that they are also called ship rats. On land, they often climb trees and utility poles. Both species are not picky about where they choose to live, though Norway rats are slightly more likely to be found in sewers and other low, wet places, while black rats are somewhat better adapted for tropical climates.