Nine states and the District of Columbia issue marriage licenses to same-sex couples, including three states -- Maryland, Washington, and Maine -- where voters approved it in ballot initiatives last year.

CNN: French lawmakers approve same-sex marriage bill

Three-quarters of the states have passed laws banning gay marriage, though some might vote against an amendment on states'-rights grounds.

ECONOMIST: Gay marriage

If history is any guide, the odds should be stacked against advocates of same-sex marriage in Washington and the three other states (Maine, Maryland and Minnesota) that will vote on the issue in November.

ECONOMIST: Gay marriage