From time to time colleagues at the International Society of Family Law would ask me to suggest a book on family law in the United States. I invariably recommended Professor Homer H. Clark’s textbook, Domestic Relations in the United States, because it is a classic. However, they wanted a book that covered the basic principles of contemporary family law but was less encyclopedic, and one that bridged the gap between scholarship and practice. One friend suggested that because my career has from time to time taken me into both these worlds, I should be the one to write the book. This is it. I began this book while I was on leave from Boston College Law School during two different years, first while I was a Visiting Fellow at All Souls College, Oxford and later as a Visiting Fellow at Pembroke College, Oxford. I wish to thank the Warden and Fellows of All Souls College and the Master and Fellows at Pembroke College for the opportunity they gave me to spend my complete time working on this book. In England I have been extremely fortunate in learning a great deal about English family law from Dame Elizabeth Butler-Sloss, Dame Ruth L. Deech, Stephen M. Cretney, and John M. Eekelaar. I am grateful to all of them for their friendship and for their many kindnesses to me. For making my leaves possible, I wish to thank Rev. William B. Neenan, S.J., Vice President of Boston College, who has been extraordinarily supportive of my research.