How to reference books for information that will be reproduced and sold?

I'm writing a learning game and taking information out of different books. Can I just reference the authors in MLA or do I need to also call for permission? Is there a good site that explains how to do this and when it is necessary to ask the publisher for permission to take information out? A few books I have say that I'm not allowed to do anything without permission. If I change half the words in a sentence of 10 words, do I need to reference where I got the information and ask permission? What are the rules?How to reference books for information that will be reproduced and sold?That sounds tricky. I don't know all the rules, but I recommend going to the library and asking one of the librarians for help. If they don't know the rules for what you're asking, they should be able to help you find the most current information available.How to reference books for information that will be reproduced and sold?You are in a tricky area and going scatter shot across several books isn't going to help. And what are people supposed to be learning - exactly what the book says or a concept that is the author's opinion (or your opinion.) There is an exception in the copyright law for educational use and fair use of snippets of text, with credits, but you want to presumably take meaningful chunks and sell the game, which gets edgy. If you can change the words and have the same effect, why don't you go to Wikipedia articles and get the public domain stuff there (with appropriate care it hasn't been messed with.)