An intelligence agency is a government agency responsible for the collection, analysis, and exploitation of information in support of law enforcement, national security, military, public safety, and foreign policy objectives.

Means of information gathering are both overt and covert and may include espionage, communication interception, cryptanalysis, cooperation with other institutions, and evaluation of public sources. The assembly and propagation of this information is known as intelligence analysis or intelligence assessment.

Intelligence agencies can provide the following services for their national governments.

• Give early warning of impending crisis;
• Serve national and international crisis management by helping to discern the intentions of current or potential opponents;
• Inform national defense planning and military operations (military intelligence);
• Protect sensitive information secrets, both of their own sources and activities, and those of other state agencies;
• Covertly influence the outcome of events in favor of national interests, or influence international security; and
• Defense against the efforts of other national intelligence agencies (counterintelligence).

There is a distinction between "security intelligence" and "foreign intelligence". Security intelligence pertains to domestic threats (e.g., terrorism, espionage). Foreign intelligence involves information collection relating to the political, or economic activities of foreign states.

Some agencies have been involved in assassination, arms trafficking, coups d'état, and the placement of misinformation (propaganda) as well as other covert and clandestine operations, in order to support their own or their governments' interests.