Don't forget that you can also stream music from Naxos, as well as read CD liner notes.
The lists to the right consist of books about a few selected 20th-century composers and their music. Use the call numbers of these books to locate even more resources.
ML 410 .C24 has the books about John Cage and his music.
You can go right to the 2nd floor of Murphy Library and find the ML 410 section to browse for composers -- they're in alphabetical order by composer.
Here is a brief list of some of the primary composers.
Notice that ML197 is a common call number. You can go to the 2nd floor of Murphy Library and browse around ML197 to find even more books about 20th-century composers.