The Williams Institute focuses on sexual-orientation law and public policy, and its website has a number of resources on same-sex marriage. Scholars from the think tank, which is based at California’s UCLA law school, participated in friend-of-the-court briefs in both March 2013 cases before they went the Supreme Court.

Rutgers’ law library posts a bibliography of legal literature on the topic.

The National Marriage Project at the University of Virginia conducts research and analysis on marriage issues. Brad Wilcox is director.

NPR has posted a timeline of significant developments in the debate from 1972 through 2012.

The National Conference of State Legislatures maintains a page on state laws defining marriage.

Mark R. Rank is a professor of social welfare at the George Warren Brown School of Social Work at Washington University in St. Louis. He is the author of One Nation, Underprivileged: Why American Poverty Affects Us All (Oxford University Press, 2004). His focus is on poverty, social welfare and economic inequalities.