Earlier this morning the Supreme Court of the United States struck down Section 3 of the Defense of Marriage Act and held that the supporters of Proposition 8 in California did not have standing to defend Prop 8 in federal court.
You can read the DOMA ruling here.
You can read the Prop 8 ruling here.
Essentially, the DOMA ruling means that the federal government must provide the same benefits to same-sex spouses as opposite-sex spouses, if the same-sex marriage has been lawfully performed. In other words, if a gay couple is married in a state that recognizes gay marriage, then the federal government will recognize that marriage on the same basis as a traditional marriage.
The Prop 8 ruling is far more complex, but the bottom line is that it likely clears the way for same-sex marriage in California. It does not, however, have any real implications for marriages outside of California.
Critically, neither ruling establishes a federal, constitutional right to same-sex marriage. Those states that have marriage amendments defining marriage as the union of a man and woman are untouched by these rulings. Those states that recognize same-sex marriage are similarly untouched.
The bottom line? The definition of marriage is reaffirmed as a matter primarily of state law, not federal law. The issue goes back to the states, and for the foreseeable future, states will continue to define the parameters of lawful marriage.