Wendy Sly MBE (née Smith, born 5 November 1959) is a British former athlete, who competed mainly in the 3000 metres.

She ran her lifetime bests in both events, 4:04.14 in the 1500 m and 8:37.06 in the 3000 m. Also that year, she won the IAAF World Women's Road Race Championships in San Diego contested over 10 km.

At her first Olympic Games in 1984 in Los Angeles, Sly won a silver medal in the 3000 metres, a race most remembered for the collision between Mary Decker and Zola Budd, with whom she had a strong rivalry.

Sly represented England again in the 3,000 metres event, at the 1986 Commonwealth Games in Edinburgh, Scotland, finishing eighth.

In 2013, she married her long-term partner, Andrew, whom she met through working together for her former university colleague and friend Sebastian Coe.