Glenn W. Olsen is professor emeritus of history at the University of Utah in Salt Lake City. He is the editor of Christian Marriage: A Historical Study.

John Trokan is an associate professor of religious and pastoral studies at the College of Mount St. Joseph in Cincinnati. He has written for the journal Christian Marriage and Family.

William P. Roberts is professor of religious studies at the University of Dayton in Ohio. He is the editor of Christian Marriage and Family: Contemporary Theological and Pastoral Perspectives.

Michael G. Lawler is a professor emeritus in theology at Creighton University in Omaha, Neb. His publications include Christian Marriage and Family: Contemporary Theological and Pastoral Perspectives.

Philip Lyndon Reynolds is professor of historical theology and a senior fellow at the Center for the Study of Law and Religion at Emory University in Atlanta. He is the author of Marriage in the Western Church: The Christianization of Marriage During the Patristic and Early Medieval Periods.

David Kinnaman is president of the Barna Group, which conducts research on religious life within the United States and around the world.

William Frey, a senior demographer at the Brookings Institution, analyzed the census data showing that for the first time fewer than half of American households are headed by married couples.

Stephanie Coontz teaches history and family studies at Evergreen State College in Olympia, Wash., and is director of research and public education for the Council on Contemporary Families, which she chaired from 2001-04. She is the author of Marriage, a History: From Obedience to Intimacy, or How Love Conquered Marriage.

ReligiousTolerance.org provides a summary page on marriage. The page includes links to information on different types of marriage, polygamy, same-sex marriage and divorce and remarriage.