In book collecting, the first edition is the earliest published form of a book. A book may have more than one first edition in cases where it has been published in multiple forms, including foreign releases or editions with substantially changed content such as an illustrated or a limited edition. Typically, the earliest version of the book is considered the first edition, with subsequent releases referred to as 'first edition thus' or 'first thus'. In collecting, first edition refers to the first printing unless a later printing is specifically stated.
Identifying first editions can often be a little more complicated than it appears, and just because a publisher states the words "first edition" does not necessarily mean the book is a first edition. To further complicate things, the implication between different points of issue is vital to identification. For more information on identifying first editions, see the article in our book collecting guide, and see this resource for more publisher-specific information on identifying first editions. Or, see this article for a more comprehensive discussion of what a first edition is.
The accompanying image is a picture of the first edition of Frank L. Baum's The Wonderful Wizard of Oz, one of the most sought after collectible children's books in history.