It has been said that "conflict is endemic to budgeting." If conflict within Congress or between Congress and the President impedes the timely enactment of annual appropriations acts or continuing resolutions, a government shutdown may occur. Along these lines, several options may present themselves to Congress and the President during high-stakes negotiations over appropriations measures. The options include coming to agreement on regular appropriations acts by October 1, the beginning of a new fiscal year; using one or more interim continuing resolutions (CRs) to extend temporary funding beyond the beginning of a fiscal year, until a point in time when negotiators make final decisions about full-year funding levels; or not agreeing on full-year or interim appropriations acts, resulting in a temporary funding gap and a corresponding shutdown of affected federal government activities. If Congress and the President pursue the second or third options, they may agree on full-year appropriations after the beginning of the fiscal year. These agreements may provide funding through regular appropriations acts—either in stand-alone or omnibus legislation—or, less commonly, through a full-year CR. Congress and the President frequently agree on full-year or interim funding without coming to an impasse. On other occasions, however, Congress and the President may not come to an accommodation in time to prevent a temporary funding gap. If a funding gap begins and funding does not appear likely to resume during the first calendar day of the gap, the federal government generally begins a "shutdown" of affected activities. The criteria for determining which activities are affected are complex, as discussed later in this report. This report discusses the causes of funding gaps and shutdowns of the federal government, processes that are associated with shutdowns, and how agency operations may be affected by shutdowns. The report concludes with a discussion of potential issues for Congress. The federal fiscal year begins on October 1. For agencies and programs that rely on discretionary funding through annual appropriations acts, Congress and the President must enact interim or full-year appropriations by this date if many governmental activities are to continue operating. If interim or full-year appropriations are not enacted into law, the interval in which agency appropriations are not enacted is called a "funding gap." In addition, a funding gap may occur if a CR's interim funding expires and another CR or regular appropriations bill is not enacted immediately thereafter. When a funding gap begins and appears likely to continue a full calendar day or longer, the federal government generally begins a "shutdown" of the affected activities. A funding gap and shutdown are distinct events, however (see Box 1 ). In general, a shutdown implies the furlough of certain personnel and curtailment of agency activities and services. There are multiple exceptions to this general process, however, as this report explains later. Programs that are funded by laws other than annual appropriations acts—such as entitlements like Social Security and other mandatory spending—also may be affected by a funding gap, if program execution relies on activities that receive annually appropriated funding. Funding gaps and government shutdowns have occurred in the past when Congress and the President did not enact regular appropriations bills by the beginning of the fiscal year. They also have occurred when Congress and the President did not come to an agreement on stop-gap funding through a CR. As noted in another CRS report, six relatively lengthy funding gaps occurred from FY1977 to FY1980, ranging from 8 to 17 full days. These funding gaps occurred before the Department of Justice issued legal opinions in 1980 and 1981 about agency activities that may continue during a funding gap. The opinions, which are discussed later in this report, were more restrictive in their implications about allowable activities during a funding gap compared to what agencies had done in the past. After FY1980, funding gaps continued to occur at times, but the durations of funding gaps shortened considerably compared to prior years. From FY1981 to FY1995, nine funding gaps occurred with durations of up to three full days. A significant exception to the trend toward shorter funding gaps occurred in FY1996. Two funding gaps and corresponding shutdowns of affected activities ensued, amounting to five full days during November 1995 and 21 full days during December 1995-January 1996. In the wake of the FY1996 experience, funding gaps did not occur again for over 17 years. Nevertheless, another relatively long funding gap began on October 1, 2013, the first day of FY2014, after funding for FY2013 expired at the end of September. A 16-full-day shutdown of affected activities followed. Subsequently, in FY2018, two brief shutdowns occurred. The two shutdowns illustrate how the time of day when funding resumes may affect choices that are made about when government operations will resume. They also illustrate some challenges related to counting the number of days that correspond to a particular funding gap or shutdown. Notably, they show, in different ways, how a shutdown can occur on a particular day, even in the absence of a funding gap. The first FY2018 shutdown began after a CR expired at the end of the day on Friday, January 19, 2018. A funding gap and shutdown ensued over the weekend. OMB directed agencies to execute plans for an orderly shutdown, and the Office of Personnel Management (OPM) indicated that a lapse in appropriations could affect agency operations with implications for whether employees should report to work on Saturday, January 20, 2018. Funding resumed on Monday, January 22, 2018, through another CR, which technically closed the funding gap for the entire day of Monday. Nevertheless, many federal agencies continued to shut down certain operations and furlough related employees on this weekday, because the CR that resumed funding was enacted during Monday evening, after working hours had already passed. OPM then announced late in the evening on January 22, 2018, that due to enactment of a CR, employees would be expected to return to work on Tuesday, January 23, 2018. The second FY2018 shutdown began after a CR expired at the end of the day on Thursday, February 8, 2018. In the hours after the CR's funding expired, OMB directed agencies to execute their shutdown plans, and OPM indicated that employees might be affected. A few hours later, in the morning of Friday, February 9, 2018, Congress and the President enacted another CR to extend funding. This prompted OMB and OPM to inform employees to come to work on the same day, that morning. From the perspective of prior OMB statements, a funding gap technically did not occur on February 9, 2018. However, given that OMB and OPM issued directions for a shutdown after funding expired, it is possible that some agency operations may have been affected in the few hours between expiration of the previous CR and enactment of the succeeding CR. The Constitution, statutory provisions, court opinions, and Department of Justice (DOJ) opinions provide the legal framework for how funding gaps and shutdowns have occurred in recent decades. Article I, Section 9, Clause 7 of the Constitution states, "No Money shall be drawn from the Treasury, but in Consequence of Appropriations made by Law." Federal employees and contractors cannot be paid, for example, if appropriations have not been enacted in the first place. Nevertheless, it would appear to be possible under the Constitution for the government to make contracts or other obligations even if it lacks funds to pay for these commitments. Several provisions of law—which commonly are referred to as the Antideficiency Act—generally prevent this from happening, however. The act, which evolved over time and is located in Title 31 of the U.S. Code , prohibits federal officials from obligating funds before an appropriations measure has been enacted, except as authorized by law. The act also prohibits federal officials from accepting voluntary services or employing personal services exceeding what has been authorized by law. Therefore, the Antideficiency Act generally prohibits agencies from continued operation in the absence of appropriations. Failure to comply with the act may result in criminal sanctions, fines, and administrative discipline including suspension without pay or removal from office. The act makes exceptions to the prohibitions on acceptance of voluntary services and employment of personal services, however, for "emergencies involving the safety of human life or the protection of property." For years leading up to 1980, many federal agencies continued to operate during a funding gap, "minimizing all nonessential operations and obligations, believing that Congress did not intend that agencies close down," while waiting for the enactment of annual appropriations acts or CRs. In 1980 and 1981, however, then-U.S. Attorney General Benjamin R. Civiletti issued two opinions that more strictly interpreted the Antideficiency Act, along with the law's exceptions, in the context of a funding gap. The Attorney General's opinions addressed "the scope of currently existing legal and constitutional authorities for the continuance of government functions during a temporary lapse in appropriations." In brief, the opinions stated that, with some exceptions, the head of an agency could avoid violating the Antideficiency Act only by suspending the agency's operations until the enactment of an appropriation. In the absence of appropriations, exceptions would be allowed only when there is "some reasonable and articulable connection between the function to be performed and the safety of human life or the protection of property." In addition, "there must be some reasonable likelihood that the safety of human life or the protection of property would be compromised, in some degree, by delay in the performance of the function in question." Apart from this broad category of "human life and property" exceptions to the act, the Civiletti opinions identified another category: those exceptions that are "authorized by law." GAO later summarized the 1981 Civiletti opinion as identifying four sub-types of "authorized by law" exceptions: Activities funded with appropriations of budget authority that do not expire at the end of one fiscal year, such as multiple-year and no-year appropriations.