The fate of President Obama's signature achievement, the Affordable Care Act (ACA), is in the hands of the nine Supreme Court justices.
People began lining up Friday for their chance to be in be inside the courtroom for the opportunity to see history unfold.
Justices are expected to kick off arguments Monday by questioning whether it is too soon to even be hearing the case, as the key part of the law actually under fire--the individual mandate, which requires all Americans purchase insurance or pay a fine--does not take effect until 2014. A lower court previously ruled that the lawsuits filed by 26 states should wait until then.
Justices will continue to hear arguments throughout the week even if they do determine the lower court was correct.
The Supreme Court is in particular focusing on two important questions: does Congress have the power to force people to buy something; and if the answer is no, and the individual mandate is struck down, does it unravel the entire health care law?
Lower courts have had mixed rulings on the individual mandate, with some ruling in favor of the mandate and others striking it down. One lower court rejected the mandate, but ruled that the rest of the law could stand.
The administration says the requirement that all citizens who can afford insurance purchase it is needed in order to implement a critical component of the ACA: that insurers cannot drop people with pre-existing conditions or raise premiums based on medical history.
The reasoning is that uninsured raise health care costs on everybody else, since they typically only seek care in emergencies. If they can't pay the cost of the treatment they receive, hospitals absorb the costs, then raise the costs of their services on those who are insured. This leads insurance companies to raise their premiums to cover their higher health care costs.
If compelled to do so, as they would be if the individual mandate stands, healthy individuals who might otherwise opt to remain uninsured would purchase insurance, allowing insurance companies to keep premiums low for everyone.
The U.S. Department of Health and Human Services say Americans making very low income who cannot afford insurance or those whose religious beliefs conflict with the mandate would not have to comply.
Opponents of the mandate say that if the law stands, Congress would be granted greater authority to dictate what Americans do with their lives.
Colorado Attorney General John Suthers likened the mandate to giving the government the authority to force citizens to buy energy-saving cars.
Legal experts have called the case the most critical since FDR's New Deal program went under review decades ago.
A ruling is expected in June.