is a Dutch former professional footballer and current manager. A former defender, De Boer spent most of his playing career with Ajax, winning five Eredivisie titles, two KNVB Cups, three Super Cups, one UEFA Super Cup, one UEFA Cup, one UEFA Champions League, and one Intercontinental Cup. He later spent five years at Barcelona, where he won the 1998–99 La Liga title, followed by short spells at Galatasaray, Rangers, Al-Rayyan and Al-Shamal before retiring.

De Boer is the third-most capped outfield player in the history of the Netherlands national team, with 112 caps. He captained Oranje to the semi-finals of both the 1998 FIFA World Cup and UEFA Euro 2000. He is the twin brother of Ronald de Boer, with whom he was a teammate at Ajax, Barcelona, Rangers, Al-Rayyan, Al-Shamal and the Netherlands national team.

After retiring from playing, De Boer went into management with the Ajax youth team and as assistant to Bert van Marwijk with the Netherlands national team. In December 2010, he took over as manager of Ajax and went on to win the Eredivisie title in his first season. In 2013, he received the Rinus Michels Award for manager of the year in the Netherlands after leading Ajax to their third successive Eredivisie title. The following year, he became the first manager to win four consecutive Eredivisie titles. He then had brief spells managing in Serie A with Inter Milan in 2016, Crystal Palace in the Premier League in 2017, and Atlanta United in MLS from 2018 to 2020. De Boer was appointed head coach of the Netherlands national team in September 2020, but left less than a year later in June 2021 after the team's disappointing Euro 2020 campaign.