When we first bought What in the World?2 it was on cassette. My children wore it out because they enjoyed listening to Diana Waring so much. Since then I have bought it on CD. The sound quality is much better and she has added more information if you can believe that! It is full of facts and information you can listen to it over and over again and still learn. She is an enthusiastic teacher who is able to capture the heart and mind of the listener. Even my "don't like history" son listens to her with expectation.