Do books have different ISBN # for each edition of the same book?

I'm looking to buy textbooks on Amazon and I don't want to buy the wrong edition. My school's website doesn't list the edition of the book, just the title and ISBN #. Would it have a different ISBN # if it were the wrong edition or does it not change??|||Different editions have different ISBNs.|||It is usuall a - no. or letter.|||I guess.