Frank de Boer (born May 15, 1970 in Hoorn, Netherlands) is a Dutch football defender. He is the twin brother of Ronald de Boer.

He is the most-capped player in the history of Dutch football, having represented his national team 112 times. He made his debut in September 1990 against Italy.

He began his career as a left back at Ajax before switching to centre back, a position he made his own for many years in the national team. After winning both the Champions League and UEFA Cup while at Ajax, he then joined Barcelona where he was unable to repeat his earlier triumphs and, in fact, suffered the ignominy of testing positive for the banned substance nandrolone. He briefly moved to Galatasaray in the summer of 2003 before joining Rangers in January 2004. He left Rangers in 2004 after Euro 2004 along with twin brother Ronald (his teammate at Ajax, Barcelona, and Rangers) to play the rest of his football in Qatar with Al-Rayyan .

De Boer was a natural leader and held the captaincy of the Dutch national team until his retirement after Euro 2004. He is considered a talented defender as what he makes up for lack of speed and pace, he makes up for in tenacity and extra work rate. De Boer performed best when partnering Jaap Stam in the Dutch national team central defence.

De Boer ended his international career in disappointing fashion after an injury forced him to be replaced in a quarterfinal game with Sweden at Euro 2004. The injury ruled him out of the semifinal match with Portugal which the Netherlands lost 2-1 to go out of the tournament.

De Boer also played for the Netherlands in the 1994 and 1998 World Cups, Euro 92, and Euro 2000. He had a memorable assist on Dennis Bergkamp's last-minute goal that beat Argentina in the quarterfinals of the 1998 World Cup.