Established to counter the technologically advanced, neo-fascist subversive organization HYDRA, S.H.I.E.L.D. remains the planet's largest and most effective force for neutralizing threats to world security and combating terrorism and alien infiltration.

The bulk of S.H.I.E.L.D.'s operations are covert, but a number involve public activities. The organization's policy prohibits it from usurping the role of the nation's armed forces by engaging in warfare on enemy soil. Domestic matters falling under the jurisdiction of the militia are coordinated jointly, with S.H.I.E.L.D. generally taking an auxiliary role, as in the case of the U.S. Army's pursuit of the Hulk. All covert operations are automatically S.H.I.E.L.D.'s province, making unnecessary coordination with the armed forces. Unlike the various national intelligence agencies, such as the CIA, Mossad and M-16, S.H.I.E.L.D. is international in membership, scope and jurisdiction. Most of the world's free countries participate in S.H.I.E.L.D. and sanction its activities on their soil.

S.H.I.E.L.D.'s founders remain anonymous; its advisers include renowned heads of state and corporate leaders. HYDRA assassins killed the organization's first director, whose identity remains classified. His replacement was CIA operative Nick Fury. As S.H.I.E.L.D.'s highest-ranking known agent, Fury oversaw daily administrative affairs and served as supreme field commander. The organization's Executive Board of Directors, whose seven members maintain their anonymity by communicating with personnel via video screen, determines S.H.I.E.L.D. policy and directives.

S.H.I.E.L.D.'s greatest drawback is that it has become so complex in its organization and vast in its operations that a single person, even Sharon Carter, Fury's successor as director, cannot personally oversee all its activities.