What is the function/purpose of intelligence agencies?

… By virtue of their control over secret information, intelligence agencies are ideally suited to provide comprehensive strategic analyses for policymakers. “The intelligence community,” writes Richard Betts, “is the logical set of institutions to provide what one may call the library function for national security: it keeps track of all sources, secret or not, and mobilizes them in coherent form whenever nonexpert policymakers call for them.” (Rovner, 2011, p. 4)

… How should we measure progress in the war on terrorism? How do we know if we are winning or losing? How do we wage counterinsurgency campaigns against elusive and amorphous enemies? How do we understand the increasingly complex relationships between nation-states, armed groups, and transnational actors? What are the long-term goals of resurgent great powers like Russia and China? How close are states like Iran to acquiring nuclear weapons? What do they intend to do with them? (Rovner, 2011, p. vii)

                Intelligence agencies exist to grapple with questions like these. They collect a staggering amount of information, synthesize reports from secret and open sources, and try to distill it into digestible analytical products for policymakers, diplomats, and military officers. When all goes well, intelligence estimates play an important role in strategic judgement, adding unique kinds of information and insight to help leaders cope with the inherent uncertainty and complexity of international politics. (Rovner, 2011, p. vii)

References

Rovner, J. (2011). Fixing the Facts: National Security and the Politics of Intelligence. Ithaca: Cornell University Press.