If a book you are looking for is not on the shelf, your first step should be to double check the information you have. Do you have the correct call number? Are you certain that the book is housed on this campus? Is the book checked out? Once you have made sure that you are looking in the right location and that the book is available to be checked out, you should check with library staff. The book may have been recently returned and has not been re-shelved yet. It may also be misshelved or being used at the moment by another student. The library staff should be able to help you track down the book you are looking for and offer suggestions for other sources that may be of use to you.