The rails (Rallidae) are a large cosmopolitan family of 140 species of small to medium-sized birds. The family exhibits considerable diversity and the family also includes the crakes, coots, and gallinules. Many species are associated with wetlands, although the family is found in every terrestrial habitat except dry deserts, polar regions and alpine areas above the snow line.

Members of the Rallidae are found on every continent except Antarctica. There are numerous island species. The most common habitats are marshland or dense forest. Rails are especially fond of dense vegetation.

The wings of all rails are short and rounded. The flight of those species that are able to fly, while not very powerful, can be sustained for long periods of time and many species undertake annual migrations. Rails often prefer to run rather than fly, especially when in dense habitat.

Many island rails are flightless because small island habitats without threatening predators often eliminate the need to fly or move long distances. Due to their tendencies towards flightlessness, many island species have been unable to cope with introduced species. The most dramatic human caused extinctions occurred in the Pacific Ocean as people colonised the islands of Melanesia, Polynesia and Micronesia, during which an estimated 750-1800 species of bird went extinct, half of which were rails. Some species which came close to extinction, such as the Lord Howe Woodhen, and the Takahç, have made modest recoveries due to the efforts of conservation organisations.