Interlibrary loan is a service that allows a you to visit your local library to borrow books, DVDs, music, etc... and/or receive photocopies of documents from almost any other library in the country.
If you've never used ILL before, it's very easy!
All you have to do is request materials from other libraries at your home library. In a few days the material that you requested arrives from the other library and you are free to check it out. This is especially important if you're looking to check out books that are out of print, rare, prohibitively expensive, or difficult to find.
Your library will act as an intermediary, identify libraries with the desired item, place the request, receive the item, make it available to you, and then arrange for its return.
The lending library usually sets a due date and overdue fees of the material borrowed. Although books and journal articles are the most frequently requested items, some libraries will lend audio recordings, video recordings, maps, sheet music, and microforms of all kinds. In some cases, nominal fees accompany the interlibrary loan services.