Normally, title and name of the author of a book is enough to locate more information about it. You can then use online bookstores or online library catalogs to identify publisher, publication date, edition and ISBN; these items are sometimes required by libraries or bookstores to order the book.
Occasionally, the author's name is misspelled, especially with foreign authors. In this case try searching for the title alone, until you find the proper spelling of the name.
If you only have the book's ISBN, you should be aware of the fact that different editions as well as hardcover and soft-cover versions of a book have different ISBNs. It is possible that the version of the book with your ISBN is already out of print, while another version is still available. It is therefore best to use an online service to get the author and title information, and then proceed with that information.
Locating a book is much more difficult if you want to educate yourself about a topic but don't have a particular author or title in mind. Library shelves are organized by subject; learn the system used by your library, go to the relevant shelve and browse the books about your topic. Some of this can also be done online: library catalogs allow subject and keyword searches and the Library of Congress permits browsing by call number, which can often locate closely related materials. For an effective subject search, you need to know which subject words are being used; this is contained in the "Library of Congress Subject Headings", a red five-volume work that many libraries have but can not be found online.
Most topics have one or two "standard references", the generally acknowledged best treatments of the subject. To find these, you need to talk to a specialist in the field. A Usenet posting to a relevant newsgroup, asking about good books, also often yields excellent results. Closely reading the user-supplied book reviews on amazon.com will also often point you to standard references: they are often only identified by author and everyone seems to know them.
You have to decide whether you want to buy the book or just read it. If you want to buy it, you have to decide whether to buy it new or used (the only option if no version of it is in print).
To buy used books, you can try a local used book store. These can also often help you buy books that they don't have. You may also go to a professional book finder with connections in the used-book markets. These used-book markets are now open to everyone with a web browser and a credit card, and books can also be found via auction websites.
A book in print can be ordered at any bookstore and can also be ordered online; several price comparison services exist. By ordering online, you typically save sales tax but you have to pay shipping and handling costs.
As to libraries, it is advisable to locate a good local college or university library. These can be used by non-students for free or for a small fee. Research librarians at these institutions are extremely capable of locating books and journal articles quickly. On campus, you can often use expensive databases such as LexisNexis for free. Libraries are connected by an Inter Library Loan network: if the book exists, you will have it in a week or so.
Libraries use WorldCat at OCLC in order to find books at other libraries. WorldCat is by far the most extensive database of library holdings, but is not directly available to the public. Some libraries allow access by their patrons; ask your librarian how to access WorldCat. Unsuccessful ABEbooks searches are directed to WorldCat as unsuccessful WorldCat searches are to ABEbooks. Data from WorldCat may be used only for limited purposes:
Library catalogs:
Acquiring information about the book
Acquiring the book
Online price comparisons:
Online booksellers:
Private auction sites:
There are also digital libraries, where you can find books in electronic form (mostly scanned paper books).