This book I purchased new and will stay a PERMANENT part of my library and I state this for very good reason. It's the first book I recommend at the mere mention of "my child does _________, why?" Written in simple terms, the layout is very easy to follow and understand. I've lent my copy to family members, friends and even read by the 10 year old I babysit when she asked me "Why does he DO THAT?!" Loved this book, and it's one that I could never part with!