From the Prop 8 Trial Tracker, which offers this helpful background:

To recap, Judge Walker ruled Prop 8 to be unconstitutional in August 2010. The case and various related cases wound they way through the courts over the next year and a half. Tomorrow, the 9th Circuit Court of Appeals will finally issue a ruling on the appeal of Judge Walker’s verdict. From there, the case could go to the full 9th Circuit en banc (full 9th Circuit rather than just a panel of judges, as is the case here) and/or the Supreme Court.