So what happens now that a shutdown is in place?
Republicans and Democrats couldn't agree on a spending plan for the fiscal year that started Tuesday as they wrangled over Obamacare, leaving federal coffers short.
Here's a quick Q&A to get you caught up on what happened and what to expect:
1. Why did the government shut down?
Congress has one key duty in the Constitution -- pass spending bills that fund the government. If it doesn't, most functions of government -- from funding agencies to paying out small business loans and processing passport requests -- grinds to a halt. But some services, like Social Security, air traffic control and active military pay, will continue to be funded. Oh, and Congress still gets paid, too.
2. Why does it have to pass a spending bill in the middle of the year?
It may be the middle of the calendar year, but the government's fiscal year runs from October 1 to September 30.
3. What was the holdup?
House Republicans insist any new spending bill include provisions to either defund, derail or otherwise chip away at Obamacare. Senate Democrats are just as insistent that it doesn't.
4. How is Obamacare tied to the spending bill?
The health care law isn't directly tied to funding the government, but it's being used as a bargaining chip. A group of Republicans, led by freshman Sen. Ted Cruz of Texas, believe the president's signature domestic policy achievement is so bad for the country that it is worth disrupting government funding to undercut it.
5. What are some of the objections to Obamacare?
The Patient Protection and Affordable Care Act, the actual name of the law, requires all Americans to have health insurance. Opponents say it'll hurt employers and amounts to overreach by the federal government. Some have also criticized the medical device tax that's part of the law, saying that by imposing such a tax, it's basically sending jobs overseas.
6. What's the Democrats' defense?
They say the law will expand access to health care and help rein in the rising costs of coverage. Obamacare prevents those with pre-existing medical conditions from being denied health insurance, and proponents say those who have health insurance will no longer have to indirectly pay for those who show up in emergency rooms uninsured.
7. What happened with the spending bill over the weekend?
The Republican-dominated House passed two spending bill amendments Sunday morning -- one that would delay Obamacare for a year and one that would repeal the Obamacare's medical device tax. The bill went back to the Senate, where Democrats who control that chamber have consistently said any changes to Obamacare would be a deal-killer.
8. What happened Monday?
The Senate rejected the latest House proposal, prompting the House to approve another spending plan that would remove the Obamacare individual mandate. The Senate rejected that, too, setting the stage for a shutdown.
9. What happened overnight?
House members voted to reaffirm the anti-Obamacare amendments that Senate Democrats have said would be a deal-breaker. They also requested a conference with the Senate to work out their differences.
10. What will happen Tuesday?
The Senate will reconvene and will likely make a decision on the House's offer to talk. But Senate Majority Leader Harry Reid said late Monday night that he wouldn't agree to such a meeting until the House presents a clean spending bill stripped of the amendments.
"We will not go to conference with a gun to our head," he said.
11. Has this happened before?