There are good reasons why almost every nonfiction book published by a traditional publisher begins with a book proposal.
The book proposal is like a business plan for your book. It’s where you map out a book’s strengths and overcome its weaknesses. It’s where you describe what the book is about, why you are writing it, the market it’s aimed at, your promotional plans and, importantly, the expertise that makes you best placed to write it.
A publisher also wants to know what your book will be saying that’s new or different from other books similar to your own. With this information a publisher will know where to place your book in the market—and whether indeed there is a market for the book.
Although the purpose of the book proposal is to sell your book idea to a publisher it’s still worth your while writing one even if you’re looking to self-publish (either yourself or via a hybrid/contract publisher). You will unveil hidden areas in your thinking and save yourself time, angst and money by doing this work for yourself.
The proposal is a road map for the journey ahead, from writing to promoting to selling your book. It forces you to think through your book in detail, and you will see that the work is worth the effort once you begin writing.