The United States Secretary of Homeland Security is the head of the United States Department of Homeland Security, the body concerned with protecting the American homeland and the safety of American citizens. The Secretary is a member of the President's Cabinet. The position was created following the terrorist attacks of September 11, 2001. The new department consisted primarily of components transferred from other cabinet departments because of their role in homeland security, such as the Plum Island Animal Disease Center, previously in the Department of Agriculture. It did not, however, include the FBI or the CIA.

Traditionally, the order of the presidential line of succession is determined (after the Vice President, Speaker of the House, and President pro tempore of the Senate) by the order of the creation of the cabinet positions, and is mandated as such under 3 USC 19. However, as of the adjournment of the 108th Congress on January 3, 2005, the Secretary of Homeland Security has not been formally written into the line of succession as it appears in the United States Code. In the 108th Congress, the Senate passed a bill, S.148, that would insert the Secretary of Homeland Security right after the Attorney General, in light of the Secretary's security and managerial responsibilities that would make the Secretary more ready to assume the Presidency than say the Secretary of Agriculture or Education. A similar bill was debated in the House of Representatives during the 108th Congress, under the designation H.R. 2319; this bill, however, never made it out of committee.

^[1] From October 8, 2001 to January 24, 2003 Tom Ridge held the office of Assistant to the President for the Office of Homeland Security, a temporary cabinet-level office that served in an interim capacity until Congress approved the new department. With the creation of the Department of Homeland Security, Tom Ridge had a change in title (following Senate confirmation).

^[2] On January 11, 2005, President Bush nominated federal judge Michael Chertoff to succeed Ridge as Secretary of Homeland Security. Bush had first nominated Bernard Kerik, former commissioner of the New York City Police Department but Kerik withdrew his nomination, citing "personal reasons."