Unmarried Equality (originally the Alternatives to Marriage Project) is a nonprofit organization that advocates for equality and fairness for unmarried people. The organization, which is based in Brooklyn, N.Y., says it does not oppose marriage but wants validation and support, including nondiscriminatory public policies, for those who are single or in nonmarital relationships.

The U.S. Census Bureau provides a summary page on marital status and living arrangements.

Psychology Today offers a summary page on marriage, including articles and blogs by relationship experts. The page also includes links to pages on related topics, including divorce, homosexuality and relationships.

The Marriage & Religion Research Institute archives data about marriage from a number of sources. It also posts links to scholars around the country.

See the Centers for Disease Control and Prevention’s summary page on marriage and divorce.

The Barna Group provides a summary page on family and kids.

ReligiousTolerance.org provides an article on marriage and divorce in Islam.

Judaism 101 provides a summary page on marriage. The page describes Jewish beliefs on topics including soul mates, a typical wedding and the marital relationship.

JewishEncyclopedia.com provides a summary page on marriage.