That's a difficult question because readers have very different tastes. While some readers may cite classics such as the Bible, Shakespeare's plays, or even the Harry Potter series, no single book has been definitively identified as the number one most read book in the world. The best we can do is look at some of the most popular books of all time, which include the Bible, The Lord of the Rings, The Little Prince, The Alchemist, and Alice's Adventures in Wonderland. Depending on which metric you use, one of these books might take the top spot for most read books ever. So, ultimately, the answer to "What is the number 1 most read book?" is up for debate.