How to Find a Book
How to Find a Book depends on how much information you have about the book and whether you want to buy it or simply read it.
Acquiring information about the book 
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 library subjects can be searched and browsed on ISBNdb.com's subject search).
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.
Acquiring the book 
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, unless you can find a new after-market copy or a remaindered book).
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 or debit card, and books can also be found via auction websites. The three best sites for used-books, which between them cover countless thousands of sellers are: Abebooks, eBay and Amazon (on an Amazon book entry look for the link to "new and used books", which takes one to many sellers of used books).
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.
Depending on what you need, you may be able to find a book at a public library or a good local college or university library. These can be used by non-students for free or for a small fee.
If your reading interest is general, or if you want to read a popular novel, a public library is the place to go. Membership is usually free. If you cannot find the book on your own, you should visit an information desk because many libraries offer the ability to place "holds" on materials so you can get them when you return.
At college and university libraries, Research librarians can help you locate books and journal articles of academic interest 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, and is held by a library willing to loan it, you will have it in as little as a week or so.
Most libraries also offer an Inter-library loan service. This means that items that do not appear in their catalog can be requested from libraries elsewhere. Depending on the library and how far the book has to travel, there may be charges for this service.
Libraries use WorldCat at OCLC in order to find books at other libraries. It is by far the most extensive database of library holdings. 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. WorldCat attempts to restrict use of its data but such terms are not legally valid under US copyright law, since only the specific and creative original expression, if any, can be protected by copyright and the right to use public domain works cannot be restricted by contract (see Feist v. Rural and Assessment Technologies v. WIREdata)
- "WorldCat® records, metadata and holdings information ("Data") may only be used by Users (individuals accessing WorldCat via OCLC Web interfaces) solely for the personal, non-commercial purpose of assisting such Users with locating an item in a library of the User's choosing. Users acquire no ownership rights to any Data or portions thereof provided in any form by WorldCat. No part of any Data provided in any form by WorldCat may be used, disclosed, reproduced, transferred or transmitted in any form without the prior written consent of OCLC except as expressly permitted hereunder. Use of WorldCat for cataloging purposes is expressly prohibited. User may not resell or otherwise transfer WorldCat. User shall not omit or obscure any notice of a limitation of warranty, disclaimer, copyright, patent, trademark, trade secret, usage limitation or any logo, splash screen or any other terms and/or conditions intended to be displayed in WorldCat by OCLC or any supplier thereto."
Library catalogs 
- COPAC, combined catalog of the British Library and UK and Irish research libraries
- California Digital Library, combined catalog of the University of California schools
- Library of Congress catalog
- Access Pennsylvania Database, provides a catalog in database form for the entire Pennsylvania library system
Digital libraries 
There are also digital libraries, where you can find books in electronic form (mostly scanned paper books). The most famous digital library is Project Gutenberg.
Digital databases 
- Google Books, searches books Google has scanned