When you buy a Leanpub book, you will get all the updates to that book for free. We call an update a new "version" of the book.

You can download the latest version of any book you have bought from your Leanpub library here: https://leanpub.com/user_dashboard/library.
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However, sometimes an author publishes a new book on the same topic as the old book. That is called a new "edition" of the old book. In that case, you need to buy the new book.
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You can contact the author of any Leanpub book to ask them for clarification on issues like this:
​http://help.leanpub.com/en/articles/3852119-how-can-i-contact-a-leanpub-author.