The government shuts down when Congress fails to pass appropriations bills or a temporary funding measure to finance government operations for the upcoming fiscal year. This failure creates a funding gap, which legally requires the government to cease all non-essential operations until new funding legislation is enacted. Essential services related to human safety and property protection continue to operate, but many government agencies close or furlough employees during the shutdown.
Shutdowns happen mainly due to political disagreements and deadlocks over budget priorities, spending levels, or policy provisions in the funding bills. When the House and Senate pass conflicting versions of appropriations bills and cannot reach compromise, a shutdown can occur. This situation is distinctively common in the U.S. presidential system where the executive and legislature are separate.