Difference between International edition of a book and a non international one
International editions are cheaper
They are sold cheaper, in English speaking countries (or countries with education in English) outside North America: India, China, etc. The content is equal to that of US/North American versions.
There are two reasons why they are cheaper:
because they are printed in cheaper version: paperback instead of hardcover, sometimes black and white
because the publisher knows he cannot sell them at their US price anyway, so they are willing to sell them at the price people will buy them (better to sell them cheaply than not at all)
Sources:
- http://www.thetextbookguru.com/2011/04/20/international-textbook-editions-a-cheaper-alternative-2/
- http://www.abebooks.com/books/Textbooks/international-editions.shtml
- http://answers.yahoo.com/question/index?qid=20080825164810AAGRN80
There was also a case about import of international edition textbooks in the US supreme court last year (http://arstechnica.com/tech-policy/2013/03/thai-student-protected-by-first-sale-supreme-court-rules/).
Also, some international versions are only to be used outside of the US. Due to them giving a software license for a certain region. (During my Physics / Maths courses, I had to use the international edition so the license was valid in EU universities.)
It can be for a variety of reasons, I think Jim stated the most important ones.
Sometimes they have been intentionally made incompatible.
I recently came across a textbook whose "international version", though having the same edition number, had different numerical values in all the homework problems! There is no possible pedagogical reason for doing this. It was clearly just intended to make it impossible for a North American student to use the (cheaper) international version, if they are assigned homework problems from the text.