Gay marriage is gaining support from the American public and several prominent politicians, but in much of the country, it is still illegal. Two big cases being heard this week by the Supreme Court could change that. (The justices will have until June to issue their rulings.) Here's what you should know:

Tuesday, March 26: Proposition 8

In November 2008, California voters approved a same-sex marriage ban known as Proposition 8. This case, Hollingsworth vs. Perry, centers around plaintiffs Kristin Perry and Sandra Stier, whose marriage at San Francisco City Hall was annulled by Proposition 8. (The state Supreme Court had ruled in the spring of 2008 that same-sex marriage was legal, creating a window of several months when thousands of gay couples got married before Proposition 8 became law.) The Supreme Court will weigh whether Proposition 8 violates the 14th Amendment's Equal Protection Clause that "no state shall ... deny to any person within its jurisdiction the equal protection of the laws."

Wednesday, March 27: DOMA

In September 1996, President Bill Clinton signed the Defense of Marriage Act (DOMA), which states that marriage must be between a man and a woman. The law, which Clinton has since renounced, will be challenged by United States v. Windsor, filed by octogenarian Edith "Edie" Windsor after the death of Thea Spyer, her partner for more than 40 years. Windsor and Spyer married once it became legal in New York, but because DOMA prevents the federal government from recognizing same-sex marriages, Windsor was forced to pay $363,053 in estate taxes that she wouldn't have had to pay if she were married to a man.

What's at stake?

"The Proposition 8 case has the chance to be a landmark decision that fundamentally changes the law and the status of gay people in America," UCLA School of Law Prof. Adam Winkler tells CBS News. The Los Angeles Times, however, notes that "the conventional wisdom among legal experts is that the court will stop short of declaring that gays and lesbians have a right to marry nationwide," possibly bringing gay marriage to California but not to states where it is currently banned.

It really all depends on how narrowly the court rules. The main options:

* The Supreme Court rules that state bans on same-sex marriage are unconstitutional. This would be the most drastic option, forcing states with prohibitions on gay marriage to recognize these unions as legal.

* The justices maintain the narrow ruling of the 9th U.S. Circuit Court of Appeals that "found Proposition 8 unconstitutional because it stripped away a previous right to marry in California," according to the Denver Post. This would make gay marriage legal in California but not anywhere else.

* The Supreme Court overturns a lower court decision, which would reinstate Proposition 8 and make same-sex marriage illegal in California.

* The justices rule that the couples who were married during that 2008 window would have their unions recognized, without guaranteeing that any other same-sex couples can get hitched.

A recent poll showing that 58 percent of Americans support gay marriage may also influence the Supreme Court's decision, says the Washington Post's Jonathan Capehart. The justices are surely aware of changing public opinion on this issue, and could either elect "to take a back seat to a political process" clearly moving toward legalizing gay marriage by ruling narrowly, or realizing that the polls make "it easier for the court to strike down DOMA and Prop 8 without feeling it is getting too far out ahead of public opinion."

The consensus is that the Proposition 8 case has more far-reaching implications than the DOMA case. "A decision striking down DOMA would allow same-sex couples to collect federal benefits in states that recognize same-sex marriage," writes Sam Baker of The Hill. "And while that would be a big step, it would still allow states to outlaw same-sex marriage."

And it's worth remembering that while a growing majority of Americans backs same-sex marriage, there is still a large and vocal slice of the country that opposes gay unions. The Wall Street Journal warns of the consequences of the Supreme Court ruling too broadly:

A same-sex marriage ukase would achieve that rare thing, harming advocates and opponents and everyone in between. Since marriage is more than an intimate relationship but an expression of legitimacy in the eyes of society, Supreme Court-mandated marriages would confer fewer benefits on gays and lesbians than would popular acceptance. Meanwhile, the Court would tell millions of Americans that their deep moral convictions are artifacts of invidious bigotry. [Wall Street Journal]