An intelligence agency is a governmental agency that is devoted to information gathering (known in the context as "intelligence") for purposes of national security and defense. Means of information gathering 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.

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

• provide analysis in areas relevant to national security;
• give early warning of impending crises;
• serve national and international crisis management by helping to discern the intentions of current or potential opponents;
• inform national defense planning and military operations;
• protect secrets, both of their own sources and activities, and those of other state agencies; and
• may act covertly to influence the outcome of events in favor of national interests

Intelligence agencies are also involved in defensive activities such as counter-espionage or counter-terrorism.

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

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