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The Federal Bureau of Investigation (FBI) was founded in 1908 under the previous name of Bureau of Investigation. It is part of the Department of Justice Office of the Director of National Intelligence and is considered the primary law enforcement agency of the U.S. The FBI’s request for funding for the government’s 2017 fiscal year is $9.5 billion. It employs just over 30,000 people

The FBI’s own description of itself:

an intelligence driven, and threat focused national security organisation with both intelligence and law enforcement responsibility that is staffed by a dedicated cadre of more than 30,000 agents, analysts, and other professionals who work around the clock and across the globe to protect the U.S. from terrorism, espionage, cyber attacks, and major criminal threats and to provide its many partners with services, support, training and leadership

Most people do not know that the FBI reports to both the attorney general and director of national intelligence.

Currently, the FBI considers its top priority to fight terrorism threat against the U.S. It also has a Counterintelligence Division the job of which is to stop efforts against the U.S. by “foreign intelligence services” The agency adds:

While the Counterintelligence Division continues to neutralize national security threats from foreign intelligence services, its modern-day mission is much broader. The FBI is the lead agency for exposing, preventing, and investigating intelligence activities on U.S. soil, and the Counterintelligence Division uses its full suite of investigative and intelligence capabilities to combat counterintelligence threats. While the details of the FBI’s strategy are classified, the overall goals are as follows:

Protect the secrets of the U.S. Intelligence Community, using intelligence to focus investigative efforts, and collaborating with our government partners to reduce the risk of espionage and insider threats.
Protect the nation’s critical assets, like our advanced technologies and sensitive information in the defense, intelligence, economic, financial, public health, and science and technology sectors.
Counter the activities of foreign spies. Through proactive investigations, the Bureau identifies who they are and stops what they’re doing.
Keep weapons of mass destruction from falling into the wrong hands, and use intelligence to drive the FBI’s investigative efforts to keep threats from becoming reality.

As part of these initiatives, the FBI also counters “economic espionage” which are efforts by overseas companies or organizations to steal information from U.S. companies and the government

The FBI’s cyber crime operations are extensive:

The FBI is the lead federal agency for investigating cyber attacks by criminals, overseas adversaries, and terrorists. The threat is incredibly serious—and growing. Cyber intrusions are becoming more commonplace, more dangerous, and more sophisticated. Our nation’s critical infrastructure, including both private and public sector networks, are targeted by adversaries. American companies are targeted for trade secrets and other sensitive corporate data, and universities for their cutting-edge research and development. Citizens are targeted by fraudsters and identity thieves, and children are targeted by online predators. Just as the FBI transformed itself to better address the terrorist threat after the 9/11 attacks, it is undertaking a similar transformation to address the pervasive and evolving cyber threat. This means enhancing the Cyber Division’s investigative capacity to sharpen its focus on intrusions into government and private computer networks.

Among the things the FBI is most well-known for is its “Most Wanted” lists  The lists currently includes the famous “Ten Most Wanted” list, and lists of terrorists, people who have committed crimes against children, kidnapping and missing persons, white collar crimes, and bank robbers and murders.

The FBI is also well known for its Uniform Crime Reporting operation. It collects and distributes huge amounts of data:

The Uniform Crime Reporting (UCR) Program has been the starting place for law enforcement executives, students of criminal justice, researchers, members of the media, and the public at large seeking information on crime in the nation. The program was conceived in 1929 by the International Association of Chiefs of Police to meet the need for reliable uniform crime statistics for the nation. In 1930, the FBI was tasked with collecting, publishing, and archiving those statistics.

Today, four annual publications, Crime in the United States, National Incident-Based Reporting System, Law Enforcement Officers Killed and Assaulted, and Hate Crime Statistics are produced from data received from over 18,000 city, university/college, county, state, tribal, and federal law enforcement agencies voluntarily participating in the program.

The leadership of the FBI includes five people who are the Director, Deputy Director, Associate Deputy Director, Chief of Staff/Senior Counselor, and Deputy Chief of Staff.  These and other senior staff oversee the FBI’s primary divisions which are the National Security Branch , Criminal, Cyber, Response, and Services Branch, Intelligence Branch , Science and Technology Branch , Information and Technology Branch , and Human Resources Branch

Finally, how the FBI’s budget broken down based on its most recent budget request:

The FY 2017 budget request proposes a total of $9.50 billion in direct budget authority to carry out the FBI’s national security, criminal law enforcement, and criminal justice services missions. The request includes a total of $8.7 billion for salaries and expenses, which will support 34,768 positions (12,892 special agents, 2,999 intelligence analysts, and 18,877 professional staff), and $783.5 million for construction.