Janet Beth Evans (born August 28, 1971) is a record-breaking American competitive swimmer.

Born in Placentia, California, Evans started competitive swimming as a child. By the age of 11 she was setting National Age Group records in the longer events. In 1987, she broke the world records in the 400, 800 and 1500 meter freestyle events. After gaining membership on the 1988 US Olympic team, she went on to win three gold medals at the 1988 Summer Olympics in Seoul, setting a new world record in the 400 meter freestyle event. From then until the end of her career, she found herself competing mainly with her younger self, with less and less success. Evans won one more gold medal at the 1992 Summer Olympics in Barcelona, after which her times, while good enough to win her membership on the 1996 US Olympic team, were no longer at the championship level. Her loss in Atlanta to Irish swimmer Michelle Smith was her final appearance in a competitive event.

Evans was distinctive for her unorthodox asymmetric ("loping") stroke and her apparently inexhaustible cardiorespiratory reserves. Slight of build and short of stature, she more than once found herself competing and winning against bigger and stronger athletes, some of whom were subsequently found to have been using performance-enhancing drugs.