The classic definition of a first edition book is the first run of a book in the same typeface or setting. If someone is selling true first editions of a book, they will normally state that it is a first edition, first printing. This means that it is the first printing run of the book, using the same typeface. A second print run of a book, even if it uses the same typeface, is not usually considered a first edition.
Book publishers have their own versions of what they consider to be first editions. Publishers can use the term first edition for their own purposes and they show little consistency in its use. They may mark the words “first edition” on the copyright page, but this may only mean that it is the first edition by the book's current publisher. It may also have had editorial comments or a foreword added, then considered by the publisher as a first edition in that particular format.
Some first editions are very rare and can sell for very high amounts. First editions of certain books are particularly valuable to book collectors. The more famous and respected the writer, the higher the price for a first edition. First editions by writers such as Jack Kerouac and Ernest Hemingway can fetch thousands of dollars when they come up for sale.
A first edition usually refers to the first commercial publication of a book in its own hard cover, even if the book has been published before, for example as a serialization in a magazine. Previous publications of a book, such as uncorrected proofs, advance copies and bound galleys, are not as valuable as the first commercial printing of the hard cover book. Small minorities in the book world believe that uncorrected proofs are the true first editions, and in some cases they can still fetch a high price.
The copyright page of a book is a good indication of a first edition. You can check for year of publication and the ISBN number. The ISBN number holds publishing information about the book and a catalog record will be held with the British Library. There will also be a set of numbers running from one to ten on the page. If the numbers are unbroken and no numbers are missing from the sequence, then you may have a first edition.
As first editions are very rare, you should be wary of counterfeit copies. Some unscrupulous dealers try and pass off fakes for high amounts of money. Similarly, signed first editions should come with certificates of authenticity. A reputable book dealer with a good reputation should be able to help if you are thinking of collecting first editions of a particular author. Not only is the process fun, but it could be a good investment for the future.