"I'm a month late, but the answer is it depends on the category. Income from the books themselves is minimal in the scheme of things. I honestly got a FANTASTIC deal, but that's not where the majority of money comes from. It comes from the speaking and consulting. Say you write a book about the next generation of advertising. Thanks to your years of research and some branding, you are now an expert(!) at advertising. And guess what? There are LOTS of companies and people willing to pay for that expertise. In addition, conferences want you to speak and are willing to offer you $10k, $20k, $50k+ (depending on your topic, notability, etc.) to speak at their conference or to their executives. There's also the sale of book rights for TV shows, films, etc. My friend Nick Bilton sold his TV rights for his book on the history of Twitter and stands to make a nice chunk of change if the show does well. Don't just go from book to book. Establish an expertise and get people to pay you to talk..." - Ben Parr