The court ruled that Congress has the power to compel individuals to purchase insurance as a tax on people who do not have health insurance.

"The individual mandate cannot be upheld as an exercise of Congress power under the Commerce Clause," Chief Justice John Roberts wrote in the majority opinion (PDF). "In this case however, it is reasonable to construe what Congress has done is increasing taxes on those who have a certain amount of income but choose to go without health insurance. Such legislation is within Congress' power to tax."

The landmark decisions end two years of legal uncertainty and clear the way for full implementation of the 906-page law. That includes establishing insurance exchanges in each state, prohibiting insurance companies from discriminating against the sick, and requiring nearly all Americans to prove on their income taxes that they carry health insurance starting in 2014.

The court struck down part of the Medicaid expansion.

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