Most of the books I edit or proofread are fiction; romance, historical, mystery, fantasy. But editing nonfiction is a nice change of pace, also. I recently proofread a great book about re-examining every aspect of one’s life in order to determine what really makes one happy, and what doesn’t belong in one’s life. It was refreshing!
I edited a book last year about the history of human rights violations. I also edited a book about Amelia Earhart. And one about the British political system.
One thing I love about editing is that I get to learn about something while I work.