Mary Slaney (born Mary Teresa Decker August 4, 1958, Bunnvale, Hunterdon County, New Jersey) is an American former track athlete. During her career, she won gold medals in the 1500 meters and 3000 meters at the 1983 World Championships, and set 17 official and unofficial world records and 36 US national records.
Mary Decker was born in Bunnvale, Hunterdon County, New Jersey. A decade later her family moved to Garden Grove in Southern California, where Decker started running. A year later, aged 11, she won her first local competition.
She joined her school athletics club and a local track club, and completely immersed herself in running, for which she would pay an injury-laden price later in her career. Aged 12, in one week she completed a marathon and four middle- and long-distance races, ending the week with an appendectomy operation.