The primary objective of the study is to provide treatment with Ipilimumab to subjects who have serious or immediately life-threatening unresectable Stage III or Stage IV melanoma, who have no alternative treatment options, and whose physicians believe, based upon available data on benefit and risk, that it is appropriate to administer Ipilimumab at a dose of 3 mg/kg induction (with re-induction, if eligible), or for eligible subjects previously enrolled in Ipilimumab studies CA184-042, CA184-078, CA184-087, MDX010-16, or MDX010-20.