If you’re planning to write a prescriptive nonfiction book — business, self-help, health, how-to — you don’t have to finish the manuscript before you can sell it to a publisher. Most of these books are sold on a book proposal alone. But a proposal isn’t just a formality. It’s a serious marketing document, and what you include (or leave out) determines whether agents and publishers take you seriously. This guide breaks down exactly what goes into a strong nonfiction book proposal so you know what you’re building toward before you write a single page.