If Congress fails to appropriate funds for the new fiscal year beginning October 1, then most of the government will be obliged to shut down and cease operations.
However, based on past practice, some national security-related activities would be exempted from the shutdown. A newly updated report from the Congressional Research Service anticipates that “many Department of Defense activities would continue, though other activities would halt.” CRS sorts through many of the relevant issues in Government Shutdown: Operations of the Department of Defense During a Lapse in Appropriations, September 26, 2013.
Update: On September 27, the Department of Defense held a press briefing on DoD planning for a possible government shutdown.
Other new and newly updated CRS reports that Congress has sought to withhold from online public distribution include the following.
Shutdown of the Federal Government: Causes, Processes, and Effects, September 25, 2013
Federal Funding Gaps: A Brief Overview, September 23, 2013
The Debt Limit: History and Recent Increases, September 25, 2013
Salaries of Members of Congress: Recent Actions and Historical Tables, September 24, 2013
Current Debates over Exchange Rates: Overview and Issues for Congress, September 26, 2013
The Overseas Private Investment Corporation: Background and Legislative Issues, September 25, 2013
Tajikistan: Recent Developments and U.S. Interests, September 25, 2013
Kenya: Current Issues and U.S. Policy, September 23, 2013
Issues in Homeland Security Policy for the 113th Congress, September 23, 2013
Funding and Financing Highways and Public Transportation, September 23, 2013