XX World Youth Day was a Catholic youth festival that started on 16 August and continued until 21 August 2005 in Cologne, Germany, commemorating the 20th anniversary of the first World Youth Day held in 1985. It was the first World Youth Day and foreign trip of Pope Benedict XVI, who joined the festival on 18 August. This meeting was decided by the previous pope, John Paul II, during the Toronto World Youth Day of 2002. The theme was "We have come to worship Him".

World Youth Day (WYD) is an event for young people organized by the Catholic Church that was initiated by Pope John Paul II in 1985. Its concept has been influenced by the Light-Life Movement that has existed in Poland since the 1960s, where during summer camps Catholic young adults over 13 days of camp celebrated a "day of community". For the first celebration of WYD in 1986, bishops were invited to schedule an annual youth event to be held every Palm Sunday in their dioceses. Nicknamed "The Catholic Woodstock", it is celebrated at the diocesan level annually—in most places on Palm Sunday from 1986 to 2020, and from 2021 on Christ the King Sunday—and at the international level every two to three years at different locations. The 1995 World Youth Day closing Mass in the Philippines set a world record for the largest number of people gathered for a single religious event with 5 million attendees. This record was surpassed when 6 million attended a Mass celebrated by Pope Francis—again in the Philippines—20 years later in 2015.