Historically, holy days of obligation were special occasions on which Catholics were obliged to attend Mass. Catholics were also encouraged to refrain from any work or involvement with commerce on these days. Early in the twentieth century, Catholics used to observe 36 holy days, in addition to all Sundays of the year. This has since been reduced to a much smaller number.
In May 2001, with permission from the Vatican, the Australian Catholic Bishops Conference decided that in Australia, the Catholic faithful should observe the following as holy days of obligation:
All Sundays of the year.
Christmas Day (December 25 – the Feast of the Nativity of Our Lord Jesus Christ)
The Assumption (August 15 – the Feast of the Assumption of the Blessed Virgin Mary)