It depends. If it's your first book, it will be a single contract for that. If the publishers like your book because it made them rich, they may offer you a futures contract.
That said, once the publisher sees you as a cash cow, they will offer you advances and contracts on an agreed-upon number of follow up works. Good luck with that, because it only applies to the very best authors/sellers.
The thing you need to keep in mind is that the publishers really don't care what kind of writer you are, just so your stuff sells and makes them money. I'm sorry to say it, but that is the craven nature of our society and our literary industry. Don't misunderstand this jaded statement. You DO have to be able to write well to keep even the most primitive readers interested. Tom Clancy is a perfect example.
First, WRITE THE BOOK. Worry about contracts later.