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.In 2009, Koster was a mainstay of the Dutch national team, which reached the semi-finals of UEFA Women's Euro 2009 in Finland.
In June 2013, national team coach Roger Reijners selected Koster for the Netherlands' squad for the UEFA Women's Euro 2013 in Sweden.