The Cabinet was established in Article II, Section 2 of the United States Constitution to provide a source of key advisors to the President. Today, the Cabinet includes the Vice President and 15 executive departments. Here's a primer on the departments, in order of their succession to the Presidency.

Department of State

Established: The Department of State was originally established by the First Congress of the United States as the Department of Foreign Affairs on July 27, 1789. The name was changed to the Department of State less than 2 months later, when Congress passed an Act to "provide for the safe keeping of the Acts, Records, and Seal of the United States, and for other purposes."

First Secretary: After spending the previous 5 years as Minister to France, Thomas Jefferson served under George Washington from 1790 until 1793. Jefferson resigned over a disagreement about whether the U.S. should support the French in the French Revolution. He wanted to back the French; Alexander Hamilton supported the British; and Washington, whose military career began with the French and Indian War, opted for neutrality.

Mission: Develop foreign policy, advance freedom, and create a secure and beneficial world for the American people and the international community.

Notable: Six men "“ Jefferson, James Madison, James Monroe, John Quincy Adams, Martin Van Buren, and James Buchanan "“ served as Secretary of State before becoming President.

Department of the Treasury

Established: Like the State Department, the Department of the Treasury was formally established by the First Congress of the United States in 1789.

First Secretary: Alexander Hamilton served under Washington from 1789-1795. During that time, he instituted a plan for paying back the country's massive war debt, which helped establish the United States' credibility abroad. Hamilton also helped establish the First Bank of the United States in 1791. Ironically, he resigned his position to join the New York bar because he wasn't making enough money.

Mission: Collect revenue (the IRS is the largest of Treasury's bureaus), produce money, and formulate economic policy.

Notable: The Treasury is responsible for producing all of the currency and coinage in the United States. The Treasury building is depicted on one side of the $10 bill; Hamilton is on the other.

Department of Defense

Established: The Department of Defense was founded with the signing of the National Security Act of 1947 by Harry S. Truman. The Act merged the Department of War, which had been established in 1789 as one of the original four Cabinet-level positions, and the Department of the Navy, and also created the United States Air Force. The new department was originally named the National Military Establishment, but the unfortunate pronunciation of its acronym prompted it to be renamed 2 years later.

First Secretary: Henry Knox was the first Secretary of War, while James Forrestal, an aviator in World War I, was named the first Secretary of Defense in 1947. Suffering from major depression, Forrestal committed suicide two months after resigning his position in 1949.

Mission: Provide the military forces needed to deter war and protect the security of the United States.

Notable: Donald Rumsfeld is both the youngest and oldest person to serve as Secretary of Defense. He was 43 when Gerald Ford named him Secretary of Defense in 1975, and after being re-appointed by George W. Bush in 2001, served until he was 74.

Department of Justice

Established: In 1870, Ulysses S. Grant signed a bill to create a Department of Justice headed by the Attorney General -- a position that dates back to the First Congress.

First Attorney General: George Washington appointed Edmund Jennings Randolph, who had previously served as Governor of Virginia, the first Attorney General of the United States on September 26, 1789.

Mission: Enforce the law and defend the interests of the United States according to the law, prevent and control crime, and seek just punishment for criminals.

Notable: The origin of the FBI can be traced to a force of Special Agents established by Attorney General Charles Bonaparte in 1908.

Department of the Interior

Established: As its seal indicates, the Department of the Interior was established on March 3, 1849, the last day of the 30th Congress, to handle domestic matters.

First Secretary: Zachary Taylor named Thomas Ewing, who had previously served as Secretary of the Treasury under William Henry Harrison and John Tyler, the first Secretary of the Interior.

Mission: Protect and provide access to our nation's natural and cultural heritage and honor our trust responsibilities to Indian Tribes and our commitments to island communities.

Notable: The U.S. Geological Survey and National Parks Service, bureaus of the DOI, were created in 1879 and 1916, respectively. The department's oldest bureau, the Bureau of Indian Affairs, manages over 66 million acres of land and was created in 1824 under the Department of War.

Department of Agriculture

Established: The Department of Agriculture was established in 1862 by Abraham Lincoln.

First Secretary: The department wasn't elevated to Cabinet status until the final year of Grover Cleveland's first term in 1889. Norman Jay Coleman, who went into farming after receiving his law degree, served as the first Secretary of Agriculture for all of 3 weeks under Cleveland before President-elect Benjamin Harrison appointed his own secretary.

Mission: Formulate policy on farming, food, and natural resources, maintain food safety, and combat hunger worldwide.

Notable: Public outrage at the unsanitary conditions at Chicago meatpacking plants described in Upton Sinclair's The Jungle prompted the 1906 Meat Inspection Act.

Department of Commerce

Established: The Department of Commerce and Labor was created in 1903, but the Department of Commerce wasn't established as it is known today until President William H. Taft split the department on his final day in office in 1913.

First Secretary: Woodrow Wilson appointed William C. Redfield, a Congressman from New York, the first Secretary of Commerce. The first Secretary of Commerce and Labor was George B. Cortelyou.

Mission: Foster, serve, and promote the nation's economic development and technological advancement.

Notable: Future President Herbert Hoover was the longest-serving Secretary of Commerce. During his 7+ years in the position, Hoover expanded the government's "Own Your Own Home" campaign, which promoted home ownership among the nation's growing workforce.

Department of Labor

Established: The Department of Labor was a bureau within the Department of Commerce and Labor until the aforementioned split of that department in 1913.

First Secretary: William B. Wilson was appointed by Woodrow Wilson (no relation) as the first Secretary of Labor and helped the United States mobilize an effective workforce to support the troops abroad during World War I.

Mission: Assure work safety, fair pay, and unemployment insurance benefits.

Notable: Frances Perkins, who served as Secretary of Labor from 1933-1945, was the first female Cabinet-level secretary in U.S. history. The Labor Department's building is named after her.

Department of Health and Human Services

Established: The Department of Health and Human Services was created in 1980 following the separation of the Department of Health, Education and Welfare, a Cabinet-level department established by Dwight D. Eisenhower in 1953.

First Secretary: Oveta Culp Hobby, a first commanding officer of the Women's Army Corps, was the first Secretary of Health, Education and Welfare.

Mission: Protect the health of all Americans and provide essential human services, especially for those who are least able to help themselves.

Notable: Patricia R. Harris, who was secretary when the department's name changed in 1980 under Jimmy Carter, was the first African-American woman to serve in a Cabinet position.

Department of Housing and Urban Development

Established: The Department of Housing and Urban Development Act of 1965, which was signed by Lyndon B. Johnson, created HUD as a Cabinet-level agency.

First Secretary: Robert C. Weaver, a Harvard graduate, became the first African-American to serve in the U.S. Cabinet when Johnson appointed him as the first Secretary of Housing and Urban Development.

Mission: Increase home ownership, support community development, and increase access to affordable housing.

Notable: President John F. Kennedy tried to establish a similar department in 1962 through legislation and his reorganization powers, but was blocked in both instances by Congress.

Department of Transportation

Established: The Department of Transportation was established on October 15, 1966, by President Johnson and consolidated 31 agencies and bureaus.

First Secretary: Under the direction of Alan Stephenson Boyd, who served in the position from 1967-1969, the DOT issued the first national safety and federal motor vehicle standards.

Mission: Ensure a fast, safe, efficient, accessible, and convenient transportation system.

Notable: Among the many responsibilities transferred to the DOT when it was established was oversight of daylight saving time.

Department of Energy

Established: President Carter established the Department of Energy in 1977 to centralize the government's energy policy in the wake of an oil crisis. The DOE was the first addition to the Cabinet in 11 years.

First Secretary: James Schlesinger, who served as Secretary of Defense under Richard Nixon and was dismissed by Gerald Ford for insubordination, was named the first Secretary of Energy.

Mission: Advance the national, economic, and energy security of the United States and promote scientific and technological innovation.

Notable: One of the DOE's first initiatives was the development of solar research. Carter remarked in 1978: "Nobody can embargo sunlight. No cartel controls the sun. Its energy will not run out. It will not pollute our air or poison our waters. It is free from stench and smog." Today, the DOE sponsors more basic research in the physical sciences than any other federal agency in the U.S.

Department of Education

Established: Carter delivered on a 1976 campaign promise to the National Education Association when he signed a bill establishing the Department of Education as the 13th Cabinet-level department in 1979. The Office of Education was previously within the Department of Health, Education and Welfare.

First Secretary: Shirley Hufstedler, who attended Stanford Law School and was one of President Ford's candidates to replace Justice William O. Douglas on the Supreme Court, was named the first Secretary of Education after she served as Judge of the U.S. Court of Appeals for the Ninth Circuit.

Mission: Foster excellence and equal access by establishing policies on federal financial aid for education, distribute and monitor financial aid, and collect data on the nation's schools.

Notable: President Ronald Reagan vowed to eliminate the Department of Education as a Cabinet-level department and appointed T.H. Bell as Secretary of Education with that goal in mind, but both men struggled to fight for its abolishment without appearing anti-education.

Department of Veterans Affairs

Established:In 1988, Reagan signed legislation that would establish the Department of Veterans Affairs as a Cabinet-level department the following year. The Veterans Administration had been operating since 1930 and the elevation to Cabinet-level status did little to change its role.

First Secretary: President-elect George H.W. Bush named Edward J. Derwinski, a World War II veteran, as the first Secretary of Veterans Affairs.

Mission: Care for the nation's veterans, issue checks for disability, education and pensions, and supervise national cemeteries.

Notable: The Department of Veterans Affairs is the nation's second-largest federal agency. In fiscal year 2008, the department provided $38.9 billion in disability compensation, death compensation, and pension to 3.7 million people.

Department of Homeland Security

Established: The Office of Homeland Security was established to foster intelligence information sharing in the aftermath of the terrorist attacks of September 11, 2001. DHS became a Cabinet-level department under George W. Bush with the passing of the Homeland Security Act in 2002 and merged 22 agencies, including the Customs Service, United States Border Patrol, Coast Guard, and Secret Service.

First Secretary: Tom Ridge, Governor of Pennsylvania, was the first Director of Homeland Security.

Mission: Secure the country and preserve America's freedoms while preparing to respond to all hazards and disasters.

Notable: FEMA, which had operated as an independent agency since 1979, was one of the agencies absorbed by DHS.