These are the most highly selling books of all time. Religious texts and non-english texts were not included. Other books in the same series were not counted. The number one selling book of all time is Don Quixote, coming in at 500 million copies. Those are some impressive numbers, for a book that is relatively foreign to modern audiences. However, no series comes close to the number of top selling books put up by the Harry Potter series. Of the top 20 Highest selling books of all time, the Harry Potter series puts up a whopping 7 books into contention. That number is made more impressive by the length of the series:7.