How to identify a first edition

Date
The publication date is the natural starting point when when it comes to appraising your book. Generally speaking you should not see dates other than the original publication date.
You may see two dates such as a copyright date and a 'First Published' date and these can differ slightly though not usually by more than a year. You may also see a different date referring to publication in another country, these are not necessarily problematic.
Printing Statement
Most publishers are helpful when it comes this and clearly state: 'Second Edition' - 'Third Impression' 'Reprinted in...' etc etc. Clearly any mention of these terms indicates a reprint. However things are often not so easy and a book can clearly state 'first edition' or 'first printed' without mention of another edition or date and still be a reprint.
Publishers often reprinted using the same plates as the first, sometimes for years afterwards.

Undated Books
If a book shows no dates at all then the balance of probability suggests it more likely to be a later edition. However, as usual, there are many exceptions. Specialised bibliographies would need to be consulted before any final decision can be made. A very useful resource in recent years is the online access to the world's reference libraries which will supply you with a publication date, and in many cases indicate whether or not that book was dated or not.

Printers Key - Number Line
A relatively new method of indicating edition status has been adopted by many publishers, that being the printers key, often referred to as the number line. This method shows a line of numbers on the copyright page, usually between 10 and 1. The sequence of the numbers varies between publishers but the basic principal remains the same (apart from a few exceptions) a first issue-edition-impression requires the presence of the number 1.For example 10 9 8 7 6 5 4 3 2 1 indicates a first printing. 10 9 8 7 6 5 4 3 2 would indicate a second printing and so forth.

Dust Wrappers - Jackets
To make life yet more difficult as well as ascertaining that status of your book you also need to do the same for the dustwrapper or jacket. As mentioned previously reprints can appear the same as firsts with differences shown only on the dw. Always check for reviews or for titles post dating the book. The published price can often be an issue when it comes to later or so called cheap editions. There are genuine issue points on some jackets that determine the printing of the book but the biggest potential problem is when later state wrappers find their way onto first edition books. This can usually be determined by rudimentary checks though specialised bibliographies may need to be consulted

Book Club Editions
Book club editions are a source of great confusion to many and are regularly mis-sold as first editions, usually out of ignorance but occasionally not ! For collectors of UK first editions this is less of a problem than it is for collectors of American editions. UK book clubs are usually clearly stated as such, there is an absence of original publisher logos, unpriced jackets etc. Very often the books are much smaller in size or indeed a completely different format.
Things are very much more complex when it comes to American firsts when a book may appear exactly the same as a first to the uninitiated. The complexities and variations are so great that it goes well beyond the scope of this article to give a definitive guide. There are some excellent publications however that can aid the collector with specific issue points and we would recommend referring to them. The other safeguard is to buy from an established and reputable dealer who can eliminate these concerns.