The book is Adopted for Life: The Priority of Adoption for Christian Families and Churches, due out from Crossway at the end of May. (The foreword is by C.J. Mahaney.)
I'll have more to say about it in due time; but suffice it to say that this is one of the best books I've read in a long, long time.
Here's an early blurb from Al Mohler:
"Thankfully, there are good books on adoption and good books on the Gospel. But, until the arrival of Adopted for Life, there has never been a book that puts the adoption of children so clearly within the context of the Gospel of Christ. Adopted for Life is one of the most compelling books I have ever read - both deeply touching and richly theological. You will never look at adoption or the Gospel in quite the same way after reading this book. How could the church have been missing this for so long?"
--R. Albert Mohler Jr.
President, The Southern Baptist Theological Seminary