More than 250,000 foreign pilgrims from 175 countries are in Sydney for the six-day event, along with a similar number of young Australians who have registered their participation.
The organisers say some half a million people are expected to attend the closing mass on Sunday, at which Pope Benedict will be the chief celebrant.
The Pope has said he will apologise to Australian victims of sexual abuse in the church, during his visit.
Broken Rites, which represents abuse victims, has a list of 107 convictions for church abuse, but says there may be thousands more victims
Meanwhile, Australia's federal court has overturned a special law introduced to prevent protestors 'annoying' Catholic pilgrims during the papal visit.
The law, passed by the state parliament of New South Wales, threatened offenders with an AU$5,500 fine.
It was challenged by activists who claimed it eroded freedom of speech.
Protestors plan to hold a rally ahead of Pope Benedict's outdoor mass on Sunday.
Click here for RTÉ.ie's exclusive coverage of World Youth Day including a photo gallery and a pilgrim's diary.
