WASHINGTON – The Supreme Court will begin hearing arguments today over President Obama’s health care overhaul, derisively labeled “Obamacare” by its opponents. A look at how the case will unfold before the court in question-and-answer form:

Q. What’s this all about?

A. The Supreme Court is hearing a challenge to the Patient Protection and Affordable Care Act, Obama’s signature domestic achievement.

Passed by Congress in 2010, its aim is to provide health insurance to more than 30 million previously uninsured Americans, while trying to restrain costs and prevent disruptions to the majority already with coverage. Opponents say the law is unconstitutional; their chief argument is that Congress does not have the power to force unwilling Americans to buy health insurance or pay a fine.

Q. When will the court get started?

A. Justices will begin hearing arguments shortly after 10 a.m. today. They will hear six hours of arguments on several issues today, Tuesday and Wednesday.

Q. When will the justices rule?

A. The court could decide any time, but complex cases argued in the spring typically produce decisions near the end of the court’s session, scheduled for late June.

Q. Is it possible that the justices won’t decide whether the law is constitutional?

A. The first issue the court is discussing is whether an obscure tax law makes it too early for the Supreme Court to get involved. If they decide that the issue is premature, then the case will be dismissed without a binding ruling from the justices.

Q. What did lower federal courts say?

A. The 11th U.S. Circuit Court of Appeals in Atlanta ruled that Congress overstepped its authority when lawmakers passed the insurance mandate.

The 6th U.S Circuit Court of Appeals in Cincinnati upheld the entire law, as did the U.S. Court of Appeals for the District of Columbia Circuit in Washington, D.C.

The 4th U.S. Circuit Court of Appeals in Richmond, Va., ruled that the question was premature and the law can’t be challenged in court until after 2015, when the first penalties for not having insurance would be paid.

Q: Who will be arguing for the law?

A: Solicitor General Donald Verrilli Jr. will argue for the government today and Tuesday. Deputy Solicitor General Edwin Kneedler will present part of the government’s case Wednesday, and Verrilli will do the rest.

Q. Who will be arguing against the law?

A. Representing Florida today will be Washington appellate lawyer Gregory Katsas. Former Solicitor General Paul Clement, now in private practice, will represent Florida on Tuesday and Wednesday. Former Justice Department attorney Michael A. Carvin will represent the National Federation of Independent Businesses.

Q. Can I go watch the arguments, or if I can’t be in Washington, can I watch on TV or online?

A. The Supreme Court does not allow live television or radio broadcasts from inside its building, so the only way Americans can see or hear the arguments live is to be inside the courtroom while lawyers and justices debate. The Supreme Court will make the audio recording of the arguments available later the same day on its website: www.supremecourt.gov/oral–arguments/argument–audio.aspx.