I checked this out from the library for my 3-year-old son, and now knock-knock jokes are our new favorite pasttime. These are really simple jokes that can be easily taught to young children. And they're in alphabetical order, which makes it easy to find a favorite joke. The illustrations are simple, clever, and just perfect for a preschooler. My son now wants Santa to bring him this book so he can have his "very own copy." Excellent!