The Supreme Court announced today that it will hear the Prop 8 case and United States v. Windsor, which challenges DOMA's Article III. Lyle Denniston summarizes what the court will consider, including why it will review "standing" – the right to bring the cases in the first place:

There is a good deal of complexity in the marriage orders, but the bottom line is this: the Court has offered to rule on Prop. 8 and on DOMA Section 3, but it also has given itself a way not to decide either case. That probably depends upon how eager the Justices are to get to the merits; if they are having trouble getting to 5 on the merits, they may just opt out through one of the procedural devices they have offered up as potentials.

He adds:

It is obvious now why the Court took as much time as it did: the selection process must have been rather challenging, and the compositon of the final orders equally so. The Court, one might say in summary, has agreed to take up virtually all of the key issues about same-sex marriage, but has given itself a way to avoid final decisions on the merits issues.

The court's orders neglected to lift the stay in California, meaning that marriage licenses cannot be granted until the case is decided. Tom Goldstein expects arguments will be made in late March, which means a decision should arrive at the end of June. Amy Howe sketches out in detail the issues at play in each case. On Windsor:

[In June,] the Second Circuit issued its decision in the case of Edith Windsor, an octogenarian from New York who married Thea Spyer, her partner of more than forty years, in Canada in 2007.  When Spyer died a few years later, she left Windsor her entire estate, which then came with the obligation to pay nearly four hundred thousand dollars in estate taxes that Windsor would not have had to pay if federal law recognized her marriage, which DOMA of course forbids.  Windsor went to court, arguing that Section 3 of DOMA was unconstitutional, and the Second Circuit (like the district court before it) agreed.

James Esseks of the ACLU hopes for a historic decision:

The two cases both involve marriage for gay couples, but they actually present quite distinct issues. Edie Windsor is already married – she just wants to stop the federal government from treating her marriage different from everyone else’s marriages. The plaintiffs in the Prop 8 case, on the other hand, want to get married. Their case presents the marriage issue to the Court full-on – Does California’s ban on marriage for same-sex couples violate the federal constitution? Our side could get a big win – marriage in all 50 states – or we could get a smaller win – marriage in California. Either win would be spectacular progress for our movement. I’m betting that the smaller win is more likely, but public opinion on this issue is changing so quickly that it’s becoming hard to predict what the Court will do in the end.