A court case expected to result in a historic ruling on same-sex marriage in the United States has begun at a federal court in San Francisco.

The case, brought by two San Francisco couples, disputes the ban on same-sex marriage in California. Gay and lesbian couples used to be able to marry in California but when 52 percent of Californians voted against same-sex marriage in a 2008 referendum, this position was reversed.

Advocates of same-sex marriage argue that the ban is discrimination and a violation of the constitution. The case will be heard by a federal court in San Francisco but it is expected that, whatever the outcome, an appeal will be lodged with the Supreme Court. This appeal decision will then apply throughout the United States.