Daphne Helena Koster (born 13 March 1981) is a retired Dutch football player, who played as a defender for Ajax in the Vrouwen Eredivisie. She also played in the American Women's Professional Soccer (WPS) for Sky Blue FC. A powerful centre back, she was the captain of both the Netherlands women's national football team and Ajax. Koster made her senior national team debut as a 16-year-old in August 1997 against Switzerland. At the time, she was playing for a boys' amateur club, SVA Assendelft, where she played until under-19 level.