Well I was poking around through the older posts, from before I joined the board. I found this one.
The Litany of the Saints is sung (or in the rare incident of a low mass recited) at the ordination of (Sub-deacons) deacons, priests and bishops. Each ordination is done within the context of the Mass. Prior to Vatican II and among some like the FSSP who use still the missal and rites used prior to Vatican II with the permission of Pope Benedict XVI (previously authorized by Pope John Paul) Minor Orders could be confirred outside of the Mass, although it was unusual.to do so outside of the Mass.
In the Early Church, both the Latin Rite and still today in the Eastern Rites, Litanies are important parts of the Liturgy. From the few existing Liturgical Books and commentaries it seems that the Kyrie (Lord Have Mercy) in the Mass was originally a much longer litany.
Litany comes from the greek meaning supplication, and was used in Pre-Chrisitan Liturgies in Judaism, and carried over into Catholic worship as was the singing of the psalms in an antiphonal form. While most litanies were probably chanted or sung during processions, which were much more common in the Early Church, they later developed a place outside of liturgical rites proper.
Here are some more popular litanies….