In most circumstances, the answer is "yes." If you're creating a nonfiction book, you should include a subtitle since it will assist readers to tie their needs to the content of your book. If headlines entice people to pick up your book, subtitles entice them to buy it. A subtitle is therefore required for a non-fiction work. Subtitles can be included in the following places: on the back cover, inside front flap, and online through Amazon and other retailers' sites. A subtitle is also required for any book that does not have an index. An index is a comprehensive listing of all topics covered in the book. Without an index, people would have to read through their friend's old high school textbooks to find what they are looking for. This is not only time-consuming but often impossible due to privacy issues. The best place to include a subtitle is at the beginning of the front flap. This way, it will catch viewers' eyes and draw them into the book. Here are some examples of books with appropriate subtitles: Cooking For Everyone, First Steps to Self-Esteem, and How to Cope With Depression.