When I pair 'collaboration' and 'writing' in one sentence, I suppose most people would think of those great writing duos, like Ellery Queen, Mary Higgins Clark and her daughter, etcetera.
But truth be told, most writers work in a collaborative process, at least for some books. I'm in the middle of that now. I am working on a proposal for a new series. It's not a cozy series, so it's vital that I get everything right the first time when we (my agent and I) approach editors. I'll get no second chance.
My first stab at it, my agent didn't like at all. We had a long conversation, and I took what she said, and what my cozy editor had said about the idea, (My agent had told her about it briefly in a phone conversation) and went back to the drawing board, rewriting everything except the central idea.
My agent read the synopsis and liked it much better, and after some rewriting I sent her the first fifty pages, the standard proposal amount of a book for an experienced published writer. She liked it a lot better, but had another reader read it, and then she did a line by line critique.
Wow... the ideas that are coming from that are so much better than my original! It will take me a little while, but the manuscript will be so much better for her extensive input. Our collaboration will never make it onto the cover, but I will be thanking her in my acknowledgements, you can bet on that. So, when you see those Acknowledgements in the front of a book, you can be sure that the writer had a collaborator (or two, or three) to significantly help form the book into that prose you love so much.