If you are adopting and you could only buy one book, get The Connected Child by Dr. Karyn Purvis.
Don't even bother checking it out from the Library, just buy it. It will be your go-to resource book for when your child is home. If you know someone that is adopting, buy it for them, unless they have a copy then don't buy it. Family and friends of adoptive families must read this as well. This book will help them to understand what the adoptive parents are dealing with and how to appropriately interact with the adoptive child.
Since being home with our daughter I have used this book hundreds of times. This book has helped our daughter connect with us and feel safe. Being home for almost 6 months now, she is now beginning to feel somewhat safe and starting to open up about her life before us. This book has given us a guide to reach out to our daughter and help her heal from her past experiences. This book is a must in the adoption community.