Poll analysis by Sarah Dutton, Jennifer De Pinto, Anthony Salvanto and Fred Backus
As the Supreme Court begins to hear oral arguments in cases involving two high-profile laws to do with same-sex marriage - California's Proposition 8 and the 1996 Defense of Marriage Act -53 percent of Americans think it should be legal for same-sex couples to marry, while 39 percent say it should not be legal.
Although public opinion on this topic has been consistent for the last few months, it has reversed markedly from as recently as a year ago. In May 2012, just after President Barack Obama announced his support for same-sex marriage, 51 percent of Americans said it should not be legal for same-sex couples to marry.
The poll suggests the extent to which people's views have changed. Thirty-three percent of Americans who now think same-sex couples should be allowed to legally marry say they once held the opposite view.
When asked why they changed their minds, one in five volunteers that personally knowing someone who is gay or lesbian was the deciding factor (20 percent). Other reasons mentioned include being more tolerant now (17 percent), more educated now (17 percent), or that is the modern way of thinking about the issue (12 percent).
Americans' awareness of gays and lesbians in their own lives has grown over the past ten years. In 2003, most Americans said they did not have a work colleague, close friend, or family member who was gay or lesbian. Today, six in 10 Americans say they do.
Knowing someone personally who is gay or lesbian appears to be an important factor in how Americans feel about the issue of same-sex marriage. While two-thirds of Americans with a close relationship to someone who is gay or lesbian think same-sex marriage should be legal, most without such a close relationship don't think so.
Most Americans under age 45 believe same-sex marriage should be legal, including 73 percent of those under 30. Americans between 45 and 64 are divided, while 52 percent of seniors do not think it should be legal.
Politically, most Democrats (63 percent) and independents (56 percent) favor legalization of same-sex marriage, while most Republicans (56 percent) do not. Still, support for same-sex marriage among Republicans has increased from just 13 percent in May 2012 (after the President announced his support of same-sex marriage) to 37 percent today.
This poll was conducted by telephone from March 20-24, 2013 among 1,181 adults nationwide. Phone numbers were dialed from samples of both standard land-line and cell phones. The error due to sampling for results based on the entire sample could be plus or minus three percentage points. The error for subgroups may be higher. This poll release conforms to the Standards of Disclosure of the National Council on Public Polls.