United States Cabinet
The United States Cabinet refers to the most senior appointed officers of the executive branch of the United States federal government.
The first Cabinet formed by President George Washington, consisted of four people; Secretary of State, Thomas Jefferson; Secretary of the Treasury, Alexander Hamilton; Secretary of War, Henry Knox; and Attorney General, Edmund Randolph.
All members of the Cabinet are nominated by the President. The United States Senate then holds a vote to either confirm or reject any nominees. This process comes from Article II, section 2 of the U.S. Constitution, which says the president "shall nominate, and by and with the Advice and Consent of the Senate, shall appoint Ambassadors, other public Ministers and Consuls, Judges of the Supreme Court, and all other Officers of the United States, whose Appointments are not herein otherwise provided for..." 
The president does have the option of making a "recess appointment" when the Senate is in between sessions, or which in recess during a session. An appointment of this type will expire at the end of the following congressional session.
Cabinet positions customarily end when the president who nominated them steps down from office. Cabinet members can be fired by the President at any time. In some cases members of the cabinet will tender their resignation if controversy arises (i.e. Donald Rumsfeld).
The current cabinet and the order of Presidential succession after the Vice President, Speaker of the House and President pro tempore of the Senate is as follows:
* The order of succession will skip anyone who is ineligible to hold the office of the President. The former Secretary of Commerce Carlos Gutierrez and Secretary of Labor Elaine Chao are not natural-born citizens, and therefore were ineligible. ** Resigned on May 30, 2014.
There are also officers of the Cabinet who do not have the title Secretary. They are: