The word Litany comes from the Latin word Litania and the ancient Greek λιτανεία - both of which get their root from the Greek λιτή meaning supplication. The history of litany can be traced back to it's original form in the Kyrie, elesion Κύριε, ἐλέησον - literally Lord have mercy which can be found throughout the Gospels (See Matthew 15:22, Matthew 17:15, Matthew 20:30, Luke 17:13 and Mark 10:46). Before the sacred Liturgy was celebrated in Latin the Kyrie was a vestige of a litany at the beginning of Mass.
Pope Gregory the Great recorded the differences between the Eastern and Western churches when singing Kyrie - the East sang it the entire time together whereas the Western church was led with the clergy and the laity responding. The Council of Vaison in 529 passed the following decree:
"Let that beautiful custom of all the provinces of the East and of Italy be kept up, viz., that of singing with great effect and compunction the 'Kyrie Eleison' at Mass, Matins, and Vespers, because so sweet and pleasing a chant, even though continued day and night without interruption, could never produce disgust or weariness".
When the epidemic raged Rome during his time, Pope Gregory the Great commanded a litany named Septiforms. By 1601 Baronius writes there were at least 80 different Litanies being circulated. To prevent abuse, Pope Clement VIII forbade the publication of any Litany except those found in the liturgical books and that of Loreto. Today there are six litanies approved for public recitation which can be found below with their historical backgrounds.