In a rather unexpected turn of events, the Supreme Court upheld, in its entirety, the health care reform law (also known as the Patient Protection and Affordable Care Act, or simply "Obamacare"). Chief Justice Roberts joined the four more liberal Justices (Kagan, Sotomayor, Breyer, and Ginsburg) in finding that Congress had the authority to pass the law under its taxing power. Someone who refuses to abide by the individual mandate and purchase health insurance is required to pay a monetary penalty, which the majority says is a form of tax Congress is authorized to impose by the Constitution.
Five Justices found that Congress did not have the power to pass the law under the Commerce Clause (the constitutional provision that gives Congress the right to regulate interstate commerce), but ultimately this doesn't change the outcome: Because the mandate is constitutional as a tax, whether it is also constitutional under a different provision is immaterial to this case (although the five Justice majority seems to limit the previously understood scope of Congress's powers under the Commerce Clause, which could certainly affect future efforts to regulate in many areas.)
Because the mandate was upheld, the Court didn't have to pick and choose among the law's other provisions. Had the mandate been found unconstitutional, the Court would have had to decide which parts of the law (if any) could be severed from the mandate and which would have to fall along with it.
The other provision the Court had to decide on was the law's use of Medicaid funding. The Court found that Congress was free to condition additional Medicare funds on a state's agreement to expand eligibility for its program, but may not take away existing funds if a state refuses to comply with new requirements.
Why is this ruling unexpected? After the oral arguments in the case, court watchers indicated that the court seemed disinclined to uphold the mandate. In the last couple of weeks, commentators have become increasingly pessimistic on the law's chances of survival: Even a survey of former Supreme Court clerks showed that a majority thought the law was doomed. That Roberts's vote created the majority -- and the traditional swing vote lately, Justice Kennedy was part of the dissent -- makes the tea-leaf reading even more interesting.