A Holy Year is a time when the Church bestows special spiritual graces on the faithful. The origin of the Holy Years are in the Old Testament which established that a Jubilee Year be celebrated every 50 years (see Leviticus Chapter 25). The Jubilee Year is a Holy Year during which the land may not be harvested, purchased properties may be returned to their original owners, and those that serve others are freed.

Following in part this idea, the Church celebrates Holy Years. The most important are those of Rome, every 25 years, and the Compostelan, but there are other smaller ones.

The Compostelan Holy Year is celebrated when the feast of St. James (July 25) falls on a Sunday. The origin of the Compostelan Holy Years appears to date from the year 1122 when it was established by Pope Calixtus II which would make the Compostelan Holy Years older than the Roman Holy Years, but some historians doubt that this is the case.

Due to leap years, Compostelan Holy Years fall every 6, 5, 6, and 11 years. The last Holy Year was 1999 and the next (after 2004) will be in 2010. The next Holy Year after that falls 11 years later in 2021. During the 21st century the following will also be Holy Years: 2027, 2032, 2038, 2049, 2055, 2066, 2077, 2083, 2088, 2094 and 2100. In the last year of the century the regular patter is broken since this is not a leap year (the last year of each century is not a leap year except when it is divisible by 400 which was the case in 2000 which was a leap year just like the year 1600 and like the year 2400 will be).