An important day for same-sex marriage is on the horizon. A pivotal Supreme Court decision that could establish whether the Constitution allows for same-sex marriage is expected to be issued before the court's term ends on June 30. With the decision expected soon, below is a look at nine facts relating to same-sex marriage.

1. A majority of states allow gay marriage already. It's currently allowed in 36 states and the District of Columbia. The Pew Research Center has a good interactive map that shows where same-sex marriages are allowed and where they are not. It also shows change in legslation over time.

2. Americans don't trust the Supreme Court on same-sex marriage. About half of Americans -- 49 percent -- "have a moderate amount of trust" in the court concerning the upcoming decision, according to a CNN poll.

3. Support for same-sex marriage is rising. A strong majority of the Americans favor allowing same-sex marriage. Fifty-seven percent favor it, while 39 percent oppose a change, according to a Pew poll earlier this month. That's the highest percentage in favor of same-sex marriage in nearly 20 years of polling, Pew reported. As recently as five years ago, more people opposed same-sex marriage than supported.

4. There are already many gay and lesbian marriages. There are about 390,000 same-sex marriages in the United States, the Washington Post reported in April. About four in every 10 same-sex couples are married, the paper reported. There are 1.2 million adults living in a same-sex domestic partnership.

5. Many same-sex couples could get married if the Supreme Court decision rules in their favor. Using U.S. Census data, the same Post article estimated there are about 183,252 same-sex households in states where marriage is not yet allowed.

6. There's a divide along party lines. The June Pew poll found 65 percent of Democrats and an identical percentage of independents favor gay marriage, while only about one-third of Republicans are in favor.

7. There are still many who strongly oppose same-sex marriage. Recently, about 40,000 pastors and church leaders signed a petition to "resist all government efforts to require them to accept gay marriage."

8. Most Americans consider same-sex marriage inevitable. The country seems to think that same-sex marriage will eventually be allowed. Seventy-two percent of Americans said legal recognition is "inevitable," according to Pew.

9. Other countries already allow gay marriage. The United States, should it make same-sex legal across the country, would join 20 other nations that allow gays and lesbians to marry across all jurisdictions.