All libraries have a catalogue of what they have in stock.
Some are in a printed format, e.g. filing cards. Others are computerised, like our own library catalogue. You can search many other library catalogues from your own computer, using the College network. Some major universities have combined their catalogues, allowing you to search more than one library catalogue at a time. Another library catalogue that will be of use is BLPC , which is the online British Library Public Catalogue.