Large sections of the US government closed down on Tuesday after Congress was unable to reach an agreement on funding for the new fiscal year because of a standoff over healthcare reforms.
Federal workers and government functions have been divided between essential and non-essential services, and the effects will be felt in various ways - some acute, others barely noticeable.
Here is a roundup of some of the impacts.
As many as 1 million federal employees have been furloughed and the knock-on effect will be felt at companies that do business with the government, such as large defense firms and other contractors.
Among the agencies with the highest furlough rates, according to plans made public this week, were the Department of Education and the Environmental Protection Agency, each expected to idle about 94 percent of workers.
Agencies deemed key to public safety or which do not rely on Congress for funding are mostly unscathed. But some small agencies have been all but shuttered.
The Federal Election Commission, which regulates campaign finance laws, said it would idle all but four of its 339 employees. The Federal Communications Commission planned to retain 38 of its 1,716 workers.
The US Supreme Court will probably operate normally, as it has during previous shutdowns, but a spokesman declined to share the high court's plans. Federal courts will remain open for about 10 business days and their status will be reassessed on or about October 15.
The Executive Office of the President planned to furlough about 1,265 staff and retain 436 as excepted workers. Among the staff retained will be 15 to provide "minimum maintenance and support" for the White House.
Department of Health and Human Services
Signup for the new US health exchanges under the Affordable Care Act has begun as scheduled. The Medicare program for older Americans will also continue largely without disruption. Across the vast department and its sub-agencies, about 52 percent of staff will be furloughed - some 40,512 workers.
Among the programs shuttered are the Centers for Disease Control's annual seasonal flu program, which tracks the path of flu outbreaks across the nation. The National Institutes of Health is not admitting new patients in most circumstances or starting new clinical trials.
National parks have been closed to new visitors, and park roads, concessions and other facilities are now being closed. Overnight visitors have been given two days to depart. This will mean a loss of 750,000 daily visitors and an economic loss to gateway communities of as much as $30m for each day parks are shut, according to the non-profit National Parks Conservation Association.
Most popular tourist spots in the nation's capital closed on Tuesday. Barricades went up around some iconic locations, including the Lincoln Memorial, the Library of Congress, the National Archives and all Smithsonian museums. The National Zoo is closed and its popular live animal webcams were taken off line. All zoo animals will continue to be fed and cared for.
All military personnel will continue on normal duty status but about half of the Defense Department's 800,000 civilian employees will be placed on unpaid leave. The Pentagon has said it will halt military activity not critical to national security.
Officials have said military personnel, who are paid twice a month, would receive their October 1 paychecks but might see their October 15 paychecks delayed if no funding deal is set by October 7.
Most Department of Veterans Affairs services will continue, including the operation of VA hospitals.
Deliveries will continue as usual because the US Postal Service receives no tax dollars for day-to-day operations. It relies instead on income from stamps and other fees to keep running.
Air and rail travelers in the United States should not feel a big impact. Security officers and air traffic controllers will continue to work as usual. The State Department's consular services will continue at home and abroad, meaning visas will be issued and passports processed for the most part - except in rare occasions when consulates are housed in government buildings closed because of the shutdown.
Most other State Department and USAID activities can be sustained at least on a "limited basis," said department spokeswoman Jen Psaki.
The shutdown idled about 97 percent of NASA's 18,000 workers. Only 550 employees were considered exempt, including two American astronauts serving aboard the International Space Station and flight directors at Mission Control in Houston.
Skeleton staff maintain key science and communications satellites. But work on new missions, including preparations to launch a Mars probe on November 18, have been suspended, said NASA spokesman Allard Beutel. Agency websites went offline and NASA newsrooms across the country were closed.
Social Security and disability checks will be issued with no change in payment dates and field offices will remain open but will offer limited services, the agency said in a communique. Online services will remain open.
Department of Agriculture meat inspectors are staying on the job. Agricultural statistical reports have ceased publication, and the important October 11 crop report could be delayed depending on how long the shutdown lasts.
USDA's main website, USDA.gov, has gone dark and has been linked to a page explaining the shutdown.
Bank regulators, including the Federal Reserve and the Consumer Financial Protection Bureau, remain open because they do not rely on Congress for funding. The Federal Deposit Insurance Corp and the Office of the Comptroller of the Currency pay for themselves and remain open.
Loans guaranteed by Fannie Mae and Freddie Mac will still be available during the shutdown. The Federal Housing Administration, which offers mortgage lenders guarantees against homeowner defaults, will continued to operate with limited staffing.
Internal Revenue Service
IRS operations are limited but underlying tax law remains in effect, the agency said. Tax payments are coming due on October 15 for the for millions of filers who requested six-month extensions on their 2012 taxes.
The IRS said outstanding tax returns must be filed by that deadline, but it will not issue refunds while the government is closed. Live customer service lines will not be staffed.