An Overview of the Major U.S. Intelligence Agencies: What is the Difference Between the DIA, NSA, CIA and FBI?

Note: Originally published March 29, 2009 (Angelia Levy/ Read the comments section, specifically the January 26, 2018 posting for links to recent resources.

A bomb just went off at an overseas U.S. Embassy. An attorney general is tanking cases in exchange for monetary kickbacks. Known terrorists have entered the United States as students. A drug company has distributed defective over-the-counter medication in the Midwest. A hacker is attempting to access military information. An assassination attempt has been uncovered in the Middle East. A South Asian country has begun to stockpile nuclear weapons.

Work room at Defense Intelligence Agency (Photo/DIA)

These are all possible scenarios that would be handled by the Defense Intelligence Agency (DIA), the National Security Agency (NSA), the Central Intelligence Agency (CIA) or the Federal Bureau of Investigation (FBI) as part of their mission to protect the United States.

All four of these agencies conjure images of sophisticated gadgetry and high-tech nerve centers, where Top Secret information is exchanged as if it were ordinary paperwork. That’s all true to some extent, but the reality of life in the intelligence world is often more mundane and filled with more uncertainty than how it is portrayed on TV.

At the core, the U.S. intelligence agencies share a mission to protect the United States, and on good days they work together toward this cause. But as individual entities, with long bureaucratic histories of their own, each of the major intel agencies also has a specific mission and culture.

Many Americans aren’t familiar with the nature of each agency’s work beyond a general understanding that they “protect our borders” or “keep America safe.” Spy buffs aside, most people living outside the Beltway have not even heard of the NSA or DIA – which is fine as far as those agencies are concerned.

The super-secret and sometimes not-so-secret work that the intel agencies perform involves gathering and analyzing information (aka “intelligence”) for national security and defense matters.

The duties break down roughly as follows: The CIA conducts foreign covert operations, counterintelligence operations, and collects and analyzes foreign intelligence for the president and his staff to aid in national security decisions. The DIA concentrates on foreign military intelligence information, including battlefield intelligence. NSA handles the making and breaking of codes, and intercepts communications from abroad. Last but not least, the FBI conducts domestic counterintelligence and counterterrorism operations in addition to its role as the lead law enforcement agency in the country.

Though the DIA, NSA, CIA and FBI have separate responsibilities, their goals are the same -to keep America and its citizenry safe from harm and danger whether the threat is domestic or foreign.


     Defense Intelligence Agency (DIA)

The Defense Intelligence Agency, according to its website, is a “Department of Defense combat  support agency that produces analyses and disseminates military intelligence information.” DIA provides information on foreign military intelligence (e.g. political assessments, troop movement, weapons distribution, military capabilities, diplomatic changes, economic issues, health concerns, etc.) that is distributed to policymakers, defense officials, combat commanders and others in the intelligence community.

Recent incidents like the Mumbai attacks and the police shooting riots in Greece would be analyzed by the DIA for any future political and/or military ramifications that might impact the security of the United States and its allies.

Over the years, the DIA has provided intelligence data on a host of issues and incidents such as the Tet Offensive in Vietnam, the taking of American hostages in Iran, the overthrow of Idi Amin in Uganda, and North Korea’s nuclear proliferation.

The DIA has five main functions of operations: 1) gather human source intelligence; 2) analyze technical intelligence (computer crunching of info); 3) distribute intelligence/reports to the Intelligence agencies; 4) provide advice and support to the Joint Chiefs of Staff with foreign military intelligence; and 5) provide military intelligence to combatant commands. Its directors are normally three-star military generals with a staff of at least 7,500 worldwide.

Before DIA, defense intelligence gathering was collected, analyzed and distributed separately by the Department of Defense (DoD), the Joint Chiefs of Staff and the Military Intelligence Board, which consisted of military and civilian intelligence officers who helped decide defense intelligence policy.

The concept of the DIA started in 1958 with the Reorganization Act, which revised the organizational structure of the DoD and U.S. foreign intelligence as a whole. In 1961 then Secretary of Defense Robert McNamara decided to proceed with the idea of having a centralized, one-stop-shop for defense intelligence information which became the DIA. There has been some dispute over why the DIA was created. Whether it was remorse over the Pearl Harbor attacks, the U.S.-Russian missile gap of the 1950s or simply to correct managerial loopholes that led to inefficient distribution of information, no one can conclude.

Though DIA currently has access to a wealth of military intelligence and works with the DoD, the Joint Chiefs of Staff and the Director of National Intelligence (principal intelligence advisor to the president), it is not an independent agency nor is it part of the presidential cabinet. The DIA, like the National Security Agency, fall under the control of the Department of Defense.

The DIA has expanded its military intelligence work to include collecting of data on counterterrorism and nuclear proliferation. At times the DIA has found itself in conflict with the CIA, recently over the existence of weapons of mass destruction in Iraq. Other instances have involved the usual Intel rivalry between the DoD and the CIA. Nevertheless, the DIA has strived to adhere to its mission statement as being the central provider of “military, defense and national intelligence.”

NSA National Security Agency (NSA)

The National Security Agency/Central Security Services, better known as the NSA is another DoD agency that deals with foreign intelligence gathering. The NSA has a higher profile than the DIA, but its work is equally as cryptic.

The NSA describes itself as “America’s cryptologic organization” that “coordinates, directs and performs highly specialized activities to protect U.S. government information systems and produce foreign signals intelligence information.”

The NSA has two primary functions: converting cryptic foreign intelligence communication into comprehensive text (codebreaking) and protecting U.S. government information systems by using cryptography (codemaking).

It operates listening posts in the United States and around the world. These posts collect information from spy satellites and sort through data signals that may have been sent via fax phone calls, or computers to get leads on potential threats. They also create and release computer viruses to disrupt enemy systems. Their powerful monitoring capability was exemplified by the 2005 discovery that the agency had been keeping records on billions of international calls and emails that originated in the United States.

The origins of the NSA began in December 1951 when then CIA Director Walter Bedell Smith sent a memo to the National Security Council, in which the director stated that “control over, and coordination of, the collection and processing of communications intelligence had proved ineffective.” The Council then completed a study on the matter that confirmed the CIA’s conclusions. In June 1952 President Truman authorized the creation of the NSA to coordinate communications intelligence.

The main difference between the NSA and the CIA, FBI and DIA revolves around how each agency gathers its intelligence information. The NSA does not have field agents who do in-person intelligence gathering who travel the globe like 24’s Jack Bauer. Instead, its employees work primarily in Fort Meade, MD with a smaller work site in San Antonio, Texas.

The NSA likes to keep a low profile, even though its name has popped up in the news over its wiretapping work. Though the NSA’s mission and bylaws state that they are only to conduct ‘foreign’ intelligence or counterintelligence, the NSA has been able to conduct some domestic surveillance that has caused concern over privacy issues.

After the Nixon Administration, it was discovered that the NSA had wiretaps on targeted Americans. In 2005, the New York Times reported that the NSA, in an “attempt to thwart terrorism,” had wiretapped the phones of many Americans who called persons outside the country without obtaining warrants.

Over the years, the NSA has expanded its work to include more non-military communications intelligence gathering to protect other federal agency computer networks from cryptologic attacks.


Central Intelligence Agency (CIA)

The Central Intelligence Agency is arguably considered the grand daddy of the United States defense intelligence community. Its work as covert overseas operatives engaging in complex national security intelligence to protect the United States has been lionized or demonized in hundreds of books and movies over the years.

Objectively speaking, the primary function of the CIA is to provide foreign intelligence information to assist the president and senior U.S. government policymakers in making decisions relating to national security.

Some of the CIA’s covert work is public knowledge such as their unsuccessful attempt to invade Cuba to overthrow Fidel Castro (aka Bay of Pigs Invasion); the agency’s arming of Nicaraguan contra rebels (Iran-Contra Affair); and attempting to poison the then Republic of Congo’s Prime Minister Lumumba. Since the September 11th attacks the agency has focused on terrorism. Accordingly, they have formed joint operation centers in more than twenty countries where U.S. and foreign intelligence officers work together to track and capture suspected terrorists and to destroy or penetrate their networks.

The impetus for the creation of the CIA, like the NSA, came about through President Truman. During WWII, the Office of Strategic Services (OSS), a precursor to the CIA, provided strategic information to aid in the war effort. Though the OSS was eliminated after the war, Truman felt that there was still a need for a focused, central intelligence organization. In 1947 he signed the National Security Act of 1947, which charged the CIA with “coordinating the nation’s intelligence activities and correlating, evaluation and disseminating intelligence affecting the national security.”

The CIA has gone through some changes since its creation, most of the changes due to scandals and adapting to a post-9/11 world. From the 1970s to the early 1990s, the CIA had been caught assassinating or attempting to assassinate foreign leaders, conducting domestic spying operations on thousands of Americans, impeding the FBI’s Watergate break-in investigation and smuggling arms as part of the Iran Contra Affair. These incidents led to initial structural changes in the CIA, such as the installation of stronger chains of commands when authorizing covert operations.

In 2004, with the creation of the Office of the Director of National Intelligence, the CIA was no longer ‘the’ source for central intelligence for the U.S. government. The CIA is still an independent agency that collects and analyzes intelligence information and conducts covert actions. However, it has been supplanted by the National Intelligence Office when it comes to directly providing the president with information on foreign intelligence communications and operations.

FBI Federal Bureau of Investigations (FBI)

The last of the four agencies responsible for protecting U.S. interests is the Federal Bureau of Investigations. Unlike the DIA, NSA and CIA, the FBI does not directly involve itself in foreign intelligence nor is it connected to the Department of Defense. It operates under the Department of Justice with a primary focus on federal criminal investigations and domestic intelligence. Its headquarters are in Washington, DC, but it has over 50 field offices across the country. The FBI also has diplomats stationed in U.S. embassies and consulates.

According to the FBI, its mission is to “protect and defend the United States against terrorist and foreign intelligence threats, to uphold and enforce the criminal laws of the United States, and to provide leadership and criminal justice services to federal, state, municipal, and international agencies and partners.”

It is viewed as the lead law enforcement agency in the United States because of its sizeable jurisdiction which allows them to investigate over 200 categories of federal crimes such crimes as government fraud, organized crime, civil rights violations, identity theft, violent gangs, domestic terrorism, kidnappings, etc. The FBI’s intelligence and investigative work has covered such incidents as the bombing of the federal building in Oklahoma City, the Patty Hearst kidnapping, the Enron bankruptcy case and mob boss John Gotti.

The idea of an FBI came about through the passage of the 1887 Interstate Commerce Act, which created a “federal responsibility for interstate law enforcement.” It wasn’t until 1908 that the Bureau of Investigation (BOI) was organized with its own staff of agents. The BOI became the United States Bureau of Investigations in 1932, the Division of Investigation in 1932 and finally renamed the FBI in 1935.

The FBI has a well-known history of being involved in high profile incidents. Between the 1920s and 1950 the FBI was involved in shoot-outs with gangsters like John Dillinger, breaking up anti-Prohibition groups, locating Nazi agents, finding communist sympathizers and taking on organized crime. There have been some missteps by the FBI such as domestic surveillance operations of 1960s civil rights groups and its operational response during the 1993 Waco Siege in Texas.

Though the FBI continues to investigate federal crimes, it has increased its involvement in national security since the September 11th attacks. Its work involves counterterrorism; counterintelligence and cyber crime. The USA Patriot Act has also allowed the FBI to conduct domestic surveillance with limited or no warrants in the interest of national security which continues to cause them and other intelligence agencies PR pain with the general public.

The duties, roles and responsibilities of the DIA, NSA, CIA and FBI are not easily defined, since their missions can and will overlap. More than likely those who work for these agencies would find themselves hard-pressed to discuss the agencies’ similarities and distinctions. Maybe the pat response that the NSA, DIA, CIA and FBI ‘keep America safe’ may not be the best response, but it’s the easiest one.

23 responses

  1. This is really helpful!! Thanks!!


  2. […] An Overview of the Major U.S. Intelligence Agencies: What is the Difference Between the DIA, NSA, CI… […]


  3. So, what credentials or experience do you have to even write this article? On a blog with articles about your favorite makeup no less. You’re not helping anyone by writing an article like this and trying to pass it off as authoritative. To all those commenting…you do know there are far better sources for this information right? It is, literally, at your fingertips.


    1. I thought about ignoring your ridiculously condescending comment to my article. However, I decided to post and respond to it as a ‘teachable moment’ for you and others of your like-minded ilk and as an FYI to my site visitors. So let me address your ‘alleged’ issues:

      1) credentials/experience/being authoritative: It’s always those who question other people’s credentials who never mention their possible, but more than likely non-existent expertise as part of their criticism. As they say ‘talk is cheap if you’re not going to back it up.’ But I digress…I haven’t professed nor pretended to be an intelligence officer or a national security expert. I am a researcher and writer who enjoys writing about topics that I find of interest, which others have found to be informative and well-researched (i.e. Media Myth & 1960 US Presidential Election, Grant Memorial). My article is simply a summary or an overview (gasp – just like in the title!) that is meant to provide people with a general understanding of the layered apparatus that constitutes the US intelligence community. Also, you don’t have to be a professional athlete to write about sports or a doctor to write about medicine, etc. You get my drift?
      2) “blog with articles about [my] favorite makeup”: I have never posted an article on my site about beauty products. So your research-faulty comment is not only incorrect, but also juvenile and idiotically sexist. But what if I had posted an article or two about make-up? Are you saying that women can’t write about lipstick and the United States’ intelligence agencies? I bet if a dude had a sports blog or website and decided to write about national security, you would have had absolutely no problem with it, which is a pretty pathetic and stereotypical way of thinking.
      3) “far better resources”: To reiterate, my article is an ‘overview’ and was written in 2009. Accordingly, I have no doubt that there are finer and/or more current resources available on the matter (examples of which are MIA in your response, which is truly not surprising). So for my visitors, below are some recommendations for those of you who would like to read more updated information on the subject.

      Thank you ‘Greg’ for giving me this opportunity to share your moronic and not-at-all-thoughtful comments so that I could provide additional information to my non-troglodyte readers.
      There’s more than the CIA and FBI: The 17 agencies that make up the U.S. intelligence community (Los Angeles Times, 7/17/2017). A nice and quick breakdown of the agencies and their functions, which I have previously mentioned in a reply to an older comment in regards to my article.

      Top Secret America: The Rise of the New American Security State (2012). Authors Dana Priest and William Arkin “fully flesh out how the Byzantine security maze actually works, breaking down its components” which makes it a good read for national security newbies and even those who consider themselves well-versed on the topic.

      What I Learned in 40 Years of Doing Intelligence Analysis for US Foreign Policymakers (Center for Study of Intelligence, Volume 55, Number 1, March 2011). A first-person account of an intelligence officer’s experience in the national security arena.

      Top Secret America: A Hidden World Growing Beyond Our Control (Washington Post Investigation, 2010). Whether you’re a pacifist, pro-military or somewhere in-between, this multimedia project by the Post will give you a lot of information about the inner workings of the United States’ intelligence community, whether you agree or disagree with the authors’ concerns about the community’s operations. Note: The ‘Top Secret America’ book was based on this online series.

      The United States Intelligence Community: Intelligence Careers (website that provides links to all the seventeen organizations/agencies along with descriptions of said agencies).

      An Overview of the Intelligence Community (information provided by the Federation of American Scientists). Discusses in a summarily fashion how/when intelligence is gathered, who “manages the community, its budget and ‘oversight and accountability.”

      Intel is a multimedia site about the United States’ intelligence community. It’s produced by the United States government for the general public, so don’t expect to see a lot of details (i.e. inner workings, contact list, etc.). The site is primarily a summary of each agency/organization’s function, their history, important highlights and facts intermixed with visuals, get-to-know-us videos and quizzes to test your knowledge.


  4. […] An Overview of the Major U.S. Intelligence Agencies: What is the Difference Between the DIA, NSA, CI… […]


  5. Kathleen Brown | Reply

    I need to share something confidential. How do I get info to the right department?


    1. Are you trying to share info to a certain govnt person or are you trying to post something publicly as a whistleblower? If you’re trying to do the latter, then I would contact Pro Publica ( since they’re known for their journalistic integrity and protecting whistleblowers’ anonymity. Here’s a list of their staff/contract information: If you need more info, feel free to reach out again.


  6. What about DEA? They are probably one of the most important intelligence agency of the US. They have the most skilled undercover agents, they work both inside and outside, they do federal law enforcement and international intelligence… Their juridiction is like NSA, not limited to USA unlike FBI, but they operate in USA as well, unlike CIA (supposedly). Like NSA, they do national and international intelligence, but unlike NSA, they also do federal law enforcement. This is actually the most powerful agency in the states. They have office in ~70 countries. ATF is also worth mentioning.


    1. The DEA (Drug Enforcement Agency) is considered part of what’s loosely known as the ‘US Intelligence Community.’ At the time I wrote my blog post/article, I decided to stick with the top tier intelligence-gathering agencies. This Los Angeles Times January 2017 article ( provides a quick rundown of the 16 agencies/members of the intelligence community – which includes the DEA.


  7. […] An Overview of the Major U.S. Intelligence Agencies: What is the Difference Between the DIA, NSA, CI… (You’re Entitled to be Wrong, 11 May 2011) […]


    1. Thanks for linking to my post 🙂


  8. Excellent writing, i did read it twice so sorry for that, i’ve passed
    it on to my friends, so with any luck they will like it as well.


  9. I hate reading time-consuming content, simply as i’ve got a small amount of dislexia, but
    i really loved this article


  10. I came from linkedin well done on a great social media campaign


  11. […] More: NSA, CIA and FBI?… “A bomb just went off at an overseas U.S. Embassy. An attorney general is tanking cases in […]


  12. […] Differences between the Major U.S. Intelligence Agencies (angelialevy) […]


  13. […] More:NSA, CIA and FBI?…"A bomb just went off at an overseas U.S. Embassy. An attorney general is tanking cases in […]


    1. Good or bad, the United States’ ‘defense of country’ government agencies overlap more than ever. I’m sure that the employees sometimes wonder where they end and the others begin. Combine that with their administrative heads jockeying for positions adds to the fluidity of the agencies’ roles.


  14. […] in the weeks and months after the event of 9/11. That effort has been contorted into a complex, multi-agency surveillance apparatus whose attention has been turned against the American people and away from the Bill of […]


    1. It is odd and sad that the United States intelligence conglomerate has expanded to supposedly protect America, but at times it has been used against its own citizens in the name of ‘protection.’ It has forced a lot of people to question the government who never thought that they would be doing such a thing because of their long-standing faith (some would say naivete) in the government’s ability to always do the right thing.


  15. | Reply

    Just what I was searching for, appreciate it for posting.


Leave a Reply to Addison Moore Cancel reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: