Turtles All the Way Down is a young adult drama novel written by American author John Green published on October 10, 2017, by Dutton Books. It is Green's fifth solo novel and his seventh overall. The novel debuted at number 1 on the The New York Times Best Seller list in the category of "Young Adult Hardcover Books" and stayed at the top for 15 weeks and remained on the list for 62 weeks.

John Michael Green is an American author, YouTuber, podcaster, and philanthropist. His books have more than 50 million copies in print worldwide, including The Fault in Our Stars (2012), which is one of the best-selling books of all time. Green's rapid rise to fame and idiosyncratic voice are credited with creating a major shift in the young adult fiction market. Green is also well known for his work in online video, most notably his YouTube ventures with his brother Hank Green.