Polls have shown a huge and rapid reversal in public opinion on gay marriage since the laws in question - the federal 1996 Defense of Marriage Act, or DOMA, and California's Proposition 8 from 2008 - were enacted. Can the nation's highest court keep pace with public opinion?
Here are some key points to help you navigate the proceedings:
Q: What were the cases that the justices heard this week?
A: Challenges to two major laws have been slowly wending their way toward the Supremes. The first, heard on Tuesday, involved Prop 8, which California voters passed to nullify its state Supreme Court's ruling to sanction gay marriages. Now, the U.S. high court's ruling could mean major changes for some 40 states that currently do not allow gay marriage, including Pennsylvania.
The other case - argued Wednesday - centers on the 17-year-old DOMA law, which aimed to prevent the spread of same-sex marriage by, among other things, denying perks such as insurance benefits for government employees, Social Security survivors' benefits to gay spouses and spousal exemptions from paying estate taxes.
Q: Could the justices rule that same-sex marriage is now permissible under the law of the land, even in socially conservative "red states?"
A: Yes, they could - but most veteran court watchers said such a broad ruling, with sweeping civil rights implications, doesn't seem likely from the conservative-tilting Roberts court.
Q: So what type of outcome is likely on DOMA?
A: On DOMA - so out of step with the current political zeitgeist that it's been renounced by the man who signed the law, former president Bill Clinton - experts predict a reversal after a lot of skeptical questioning by the justices.
Although it was Justice Ruth Bader Ginsburg who grabbed headlines by questioning why same-sex spouses should be "this sort of skim-milk marriage," more important was that the swing vote on the court, Justice Anthony Kennedy, repeatedly questioned why the federal government could regulate marriage, traditionally a state function.
Q: What kind of ruling is likely on state bans such as California's Prop 8?
A: This is where it gets trickier. After listening to Tuesday's arguments, many experts say the court appeared to be setting the stage for a very narrow ruling - perhaps questioning whether the private citizens who are defending the California law have legal standing to bring the case.
Such a ruling - or a similarly narrow decision - would mean that gay marriage would become legal in the nation's largest state, since that would uphold an earlier appeals court ruling invalidating the 2008 anti-gay-marriage vote.
Q: What's the real upshot of this week?
A: Although a sweeping affirmation of same-sex marriage would be historic, more likely is a narrow decision that will allow the current slow march of approval of gay nuptials - with public approval at 58 percent and rising, and as more lawmakers get on board.
As for the Supremes, they may be hearing the famous choices laid out by Chrysler's Lee Iacocca, to "lead, follow, or get out of the way."
They may look at the thundering Gay Marriage Express . . . and get out of the way.
On Twitter: @Will_Bunch