Main Core is an alleged American government database containing information on those believed to be threats to national security.^[1]

The existence of the database was first asserted in May 2008 by Christopher Ketcham^[2] and again in July 2008 by Tim Shorrock.^[3]

The Main Core data, which is believed to come from the NSA, FBI, CIA, and other sources,^[1] is collected and stored without warrants or court orders.^[1] The database's name derives from the fact that it contains "copies of the 'main core' or essence of each item of intelligence information on Americans produced by the FBI and the other agencies of the U.S. intelligence community".^[1]

As of 2008^[update], there were allegedly eight million Americans listed in the database as possible threats, often for trivial reasons, whom the government may choose to track, question, or detain in a time of crisis.^[4][5]

• Disposition Matrix
• Rex 84
• FBI Index
• Investigative Data Warehouse
• National Security and Homeland Security Presidential Directive
• NSA warrantless surveillance controversy
• PRISM (surveillance program)