A shutdown occurs when the Federal Government runs out of money.

The U.S. Government budget routinely contains funds that run through midnight of October 1. If Congress does not approve and the President does not sign bills approving new funding, then certain functions will not continue and certain people will not get paid as they usually do.

Many federal employees are usually on temporary leave, meaning that they won't get paid for the time that they're not working, because they agencies they work for will not be open for business.

Most Government Departments have contingency plans, including everything from laying off employees to closing facilities. National Parks are usually the most prominent of the closings. Processes delayed usually include visa applications. NASA operations will be shut, except for vital systems supporting the crew currently aboard the space station.

Among the federal agencies or groups that are usually still open for business because their operations have been deemed too essential to be suspended are the following:

Veterans still get their veteran benefits, and retirees still get their allotments from Social Security, Medicare, and Medicaid.