Here's what we do know:
* Early Forms: Early forms of pop-ups likely existed in medieval manuscript illustrations, using flaps or cutouts to add depth and movement.
* 18th Century: Some historians believe a book called "The Mechanical Exercises, or the Art of Drawing, Writing, and Working All Sorts of Curious Devices" (1743) by William Russell could be considered the first true pop-up book.
* 19th Century: The 19th century saw more elaborate pop-ups, often used for educational purposes or as entertainment for children.
* 20th Century: The 20th century saw pop-up books becoming increasingly popular, with artists like Robert Sabuda and Matthew Reinhart pushing the boundaries of the genre.
Therefore, while a definitive "first" pop-up book is difficult to pinpoint, the earliest documented examples date back to the 18th century.