The U.S. federal government has shut down after Republicans and Democrats in Congress failed to resolve a budget dispute.
The impasse affects funding for government operations through October and beyond, and is set to cause widespread disruption for Americans in areas ranging from air travel to zoo visits.
The political stalemate is expected to put 40% of the federal workforce — about 800,000 people — on unpaid leave.
Here's how its impact will be felt across the country.
The federal flight shutdown will affect travelers in a variety of ways, potentially leading to long security lines and delays, caused by unpaid air traffic controllers choosing to stay home rather than work for free.
Air Traffic Control Agency and Transportation Security Administration (TSA) employees are considered "essential", so they will continue to go to work in the event of a shutdown.
But they will not be paid until the shutdown is over. During the last shutdown in 2018-2019, these workers increasingly took time off for medical reasons.
The impact will also be felt by Americans planning to travel abroad, with U.S. passport agencies warning that processing travel documents could take longer than usual.
No work — or pay — for federal employees
Federal employees are expected to be the hardest hit, as they will not receive any pay while the shutdown continues.
Some workers may choose to take on second jobs, as they have done during previous shutdowns. Employees who are not considered essential will be forced to stay home. In the past, these workers have been paid back.
Several agencies, such as the Centers for Disease Control and Prevention and the National Institutes of Health, are likely to lay off large numbers of workers, which would affect ongoing research and experiments already underway.
President Donald Trump, who has slashed government spending and cut federal jobs since taking office, has repeatedly warned that a government shutdown could accelerate further cuts and allow him to cut services and programs that he says are important to Democrats.
National parks without staff
Federal lands, including national parks and national forests, have been closed to visitors during past shutdowns as rangers and other employees were asked to stay home.
During the most recent government shutdown, the Trump administration decided to keep parks open, with few or no federal employees to serve them.
According to park advocates, the decision has led to vandalism in the parks as visitors drive through protected landscapes, loot historic sites and litter unchecked.
A group of more than 40 former park superintendents has written to the White House calling for the parks to be completely closed if they are shut down.
"We don't leave museums open without curators, or airports without air traffic controllers - and we shouldn't leave our national parks open without National Park Service employees," said Emily Thompson of the Coalition to Protect America's National Parks.
Zoo visits
The Smithsonian Institution's famous museums in Washington will remain open at least until next Monday, October 6.
On The Smithsonian's website said it had funds from years ago to help it stay open.
Animals at the National Zoo "will continue to be fed and cared for," according to the Smithsonian, which operates the zoo.
But popular webcams will be turned off because zoo officials consider them nonessential.
The shutdown of broadcasts will prevent viewers from watching the zoo's pandas, lions, elephants and naked mole rats.
Health care for the elderly and poor
Medicare and Medicaid, social health programs for the elderly and poor, will continue, but staffing shortages could lead to disruptions to certain services.
Emergency disaster relief is also not expected to be largely affected, but other work performed by disaster agencies will be affected.
The National Flood Insurance Program will be shut down, which will delay some mortgages on properties that require policies from the government-run program.
But if the government shutdown drags on, the Federal Emergency Management Administration (FEMA) could run out of money for its Disaster Relief Fund.
Food assistance programs will also be affected, with the Supplemental Nutrition Assistance Program for Women, Infants, and Children (WIC) expected to quickly run out of funds.
The Supplemental Nutrition Assistance Program (formerly known as food stamps) is expected to last longer, but is at risk of running out of funding.