World Youth Day 2008 was a Catholic youth festival that started on 15 July and continued until 20 July 2008 in Sydney, Australia. It was the first World Youth Day held in Australia and the first World Youth Day in Oceania. This meeting was decided by Pope Benedict XVI, during the Cologne World Youth Day of 2005. The theme was "You will receive power when the Holy Spirit comes upon you".

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.