"In a complex decision, the court found that Congress’ powers to regulate commerce did not justify the mandate. But it reasoned that the penalty, to be collected by the Internal Revenue Service starting in 2015, is a tax and is not unconstitutional.
Chief Justice Roberts, in the majority, said that the mandate was unconstitutional under the Constitution’s commerce clause. But that did not matter if the penalty that enforces it was constitutional on other grounds.
Those who elect not to buy the private insurance will pay a fine, to be collected by the IRS. This will presumably go fund medicaid and medicare. Its been a surprise that Chief Justice Roberts split with the conservatives and joined the 4 liberal justices in this ruling, for reasons described above. This ends the US status as the only major industrialized nation with a large number of uninsured people.