The American cockroach (Periplaneta americana), also known as the waterbug, or misidentified as the palmetto bug (see Florida woods cockroach for the differences), is the largest species of common cockroach, and often considered a pest. None of the Periplaneta species are endemic to the Americas; despite the name, P. americana was introduced to the United States from Africa as early as 1625. They are now common in tropical climates because human activity has extended the insect's range of habitation, and global shipping has transported the insects to world ports including the Southern United States, Tenerife, southern Spain, Greece, Taiwan, and Cape Town and Durban, South Africa.

American cockroach adults grow to an average length of around 4 centimetres (1.6 in) and about 7 millimetres (0.28 in) tall. They are reddish brown and have a yellowish margin on the body region behind the head. Immature cockroaches resemble adults except that they are wingless.

The insect can travel quickly, often darting out of sight when someone enters a room, and can fit into small cracks and under doors despite its fairly large size. It is considered one of the fastest running insects.