The Roud Folk Song Index and Broadside Index can now be found online via the Vaughan Williams Memorial Library: Roud Indexes.

From the site:

Folk Song Index

The Folk Song Index seeks to provide details of English-language traditional songs which have been recorded in any medium - books, journals, newspapers, manuscript collections in public and private hands, published or unpublished sound recordings, videos, websites, and so on.

Entries in the index are made on a one-to-one basis. If a song sung by a particular singer appears on a record, it is given an entry in the index. If the same recording is issued on a different record, it gets another entry. If the song is then transcribed in a book, another entry is created. And so on. Cross references are given when possible, but users should be aware that the number of times a song appears in the index is not an exact indication of how many times it has been collected.

Roud numbers

Roud numbers are assigned to songs to help with both identification and location and to counter the problems of multiple and variant titles. Thus, the song 'Seeds of Love' has been assigned the Roud Number three, and a search on this number will bring up all versions, whatever the title, wherever found.

The classification of folk songs is far from straightforward and a numbering scheme such as this is a blunt instrument designed to be practical rather than academically sound.

[much more about the numbering/classification system here]

Relationship with the Broadside Index

Once a song has been identified as qualifying as a 'folk song', entries for non-traditional versions (eg broadside printings) are copied from the Broadside Index into the Folk Song Index, in order to ensure that the latter remains one-stop-shop for details of traditional songs.

Broadside Index

Originally designed as an adjunct to the Folk Song Index (see above) to aid with historical research in that field, the Broadside Index has now achieved a life, and importance, of its own.

Coverage

The bulk of the entries in the Broadside Index comprises references to songs published on printed street literature trade (late 16th to late 19th centuries) in the form of broadsides, chapbooks, and cheap songsters. But coverage has been extended to include a much wider range of popular and vernacular songs including, in particular, eighteenth century songbooks and nineteenth century music hall publications. Originally envisaged as covering Britain and Ireland, material from across the English-speaking world is now included. The cut-off date is about 1920.

~ Becky in Long Beach