The U.S. government has kept secrets from the very beginning. In 1774, members of the Continental Congress passed a resolution “that the doors be kept shut during the time of business” and “to keep the proceedings secret, until the majority shall direct them to be made public.”

Secrets are even baked into the Constitution. Article 1, Section 5 says that Congress “shall keep a Journal of its Proceedings, and from time to time publish the same, excepting such Parts as may in their Judgment require Secrecy.”

In the 20th century, secrecy became synonymous with “national security” and was aimed at keeping military information out of the hands of foreign enemies. Right before World War II, informal secrecy protocols were codified and the nation was introduced to the three now-famous “classification” levels: “Confidential,” “Secret” and “Top Secret.”

Today, government officials produce classified documents at a rate of 90 million a year, or three per second. A small portion of those documents and other materials are labeled “Top Secret” because, if leaked, they have the potential to cause “exceptionally grave damage” to national security.

The Classification Levels, Explained

As the United States prepared to enter World War II, President Franklin D. Roosevelt issued Executive Order 8381, making it a crime to photograph or sketch any U.S. military installations or documents labeled “Secret,” “Confidential” or “Restricted,” which were classifications already being used by the Army and Navy.

But the first attempt to publicly define those classifications came in 1951 with President Harry Truman’s Executive Order 10290, which added a fourth category, “Top Secret,” and laid out a clear system for identifying, labeling and safeguarding highly sensitive information.

According to Truman, the classification “Top Secret” should be restricted to material that “plainly requires the highest degree of protection” and, if disclosed without authorization, “would or could cause exceptionally grave danger to the national security.”

Today, there are just three classifications (“Restricted” was dropped in 1953), each defined by the degree of “damage” the material could cause:

● “Top Secret” information “could be expected to cause exceptionally grave damage to the national security”

● “Secret” information “could be expected to cause serious damage to the national security”

● “Confidential” information “could be expected to cause damage to the national security”

What Type of Information Is Classified?

All kinds of information and materials meet one of the above standards, says Larry Pfeiffer, a former intelligence official who served as senior director of the White House Situation Room and chief of staff to the director of the Central Intelligence Agency. “Fundamentally, it all boils down to what damage could happen to national security if that information was in the hands of people who didn’t have a need to know.”

Most classified material comes from the intelligence community (FBI, CIA, NSA), says Pfeiffer, “but there’s also classified information about weapons design, diplomatic activities, and the movements of senior officials.” So not only do agencies like the FBI and CIA classify documents, but so do the Department of Defense, the State Department, the White House and more.

There are currently 1.3 million Americans with “Top Secret” clearances, including outside contractors for the Department of Defense and other agencies. But there are also “Top Secret” documents that are restricted to just hundreds or even dozens of individuals. Those documents are marked with additional labels like “SI” for “Special Intelligence” or “SAP” for “Special Access Programs.”

“Those materials are often derived from particularly sensitive human sources,” says Pfeiffer, now director of the Michael V. Hayden Center for Intelligence, Policy and International Security at George Mason University. “For example, people who were spying against their own country on our behalf.”

Disclosing those sources could put lives at risk.

Who Decides Which Documents to Classify?

Not everybody in government has the power to classify information. There are individuals who have “original classification authority,” a power granted to top-level officials in every agency and branch of government. Those original classification authorities can then delegate that power to others in their agency.

Jeffrey Fields, an international relations professor at the University of Southern California, worked as an analyst at both the State Department and the Department of Defense. He remembers drafting documents with his colleagues when the question was raised: should this be classified?

“You can’t make that unilateral decision,” says Fields, “You go to the people in your agency with classification authority and they decide.”

The president, however, has “the ultimate classification and declassification authority,” says Pfeiffer. The president is the only person with access to all levels of classified documents, and who can unilaterally decide if a document should be labeled “Top Secret” or made public.

“The most prominent example I can think of is when President Obama declassified the number of nuclear weapons in the U.S. arsenal,” says Fields. “He decided it was something the American people should know, and he wanted to show that the numbers were coming down as part of his non-proliferation initiatives.”

Handling Classified Documents Is Serious Business

To get a security clearance to view “Top Secret” information, staff members at government agencies must pass extensive background checks. The president, vice president, and members of Congress have “Top Secret” clearances on the merit of being elected by the American people, says Pfeiffer. No background checks required.

Situation Room, White House West Wing
Chip Somodevilla/Getty Images
The main conference area of the White House Situation Room.

Fields says that staffers with “Top Secret” clearances also received repeated training on how to securely handle classified information.

“From day one, it’s impressed upon you how serious this is,” says Fields. “How to store classified documents. How to transport them. How to destroy them. Everybody was definitely afraid of mishandling or accidentally leaving a document somewhere.”

To access a classified document, image or other media, individuals need to be inside what’s called a SCIF (Sensitive Compartmented Information Facility). Fields says that when the CIA came to brief his team on classified information, they would go to a secure room in the building designated as a SCIF.

The Situation Room is the highly-secure SCIF within the White House where the president receives his daily briefing from the CIA. The staff of the Situation Room is also responsible for disseminating information about breaking “Top Secret” developments—“things that need to be brought to the attention of the president and the national security advisor in minutes,” says Pfeiffer, who ran the Situation Room for two years under President Obama.

When not in use, classified documents are supposed to be returned to a safe or a special tamper-proof filing cabinet.

Declassification Is Also Part of the System

Classified documents aren’t supposed to remain under wraps forever, even “Top Secret” information. The original classification authority is supposed to place an “expiration date” on the information with a maximum of 25 years for the most sensitive documents.

“We have billions and billions of classified documents out there, many of which don’t need to be classified anymore,” says Pfeiffer. “The sources aren’t at risk of being compromised.”

The problem is that somebody needs to read each and every page of those documents to determine if they’re safe enough to be made public. That daunting task goes to the National Declassification Center, located at the National Archives and Records Administration. The staff is currently working through a 400-million-page backlog exclusively of documents 25 years or older.

“All of the executive orders say that we need to declassify more classified documents automatically,” says Pfeiffer, “but Congress never affords the resources to get it done.”

According to one analysis, the budget for declassifying documents equals 1 percent of the money earmarked for keeping government secrets.

HISTORY Vault: Great Spy Stories of the 20th Century

Delve into celebrated espionage cases of the 20th century involving spies, moles, dead drops, disguises, gadgets and more.