It's a combined volume, which means it has three books in one (cheaper price that way!).
One of the special features of Usborne books is the bite-size chunks of knowledge. A child can open up this book to any page, start anywhere on that page, and learn something! With the many headings and large text-to-picture ratio, there's always a definite beginning and ending to information. One doesn't feel overwhelmed by the text. Love it!