The definition of intelligence—the kind concerned with national security and practiced by national governments—has evolved dramatically over the decades. From Thomas Troy’s 1991 minimalist assertion that intelligence is simply "knowledge of the enemy," to the expansive, seventy-plus word definition found today on the website of the Office of the Director of National Intelligence (DNI), the field has matured both in scope and complexity, meeting the demands of the modern era by recognizing the wide array of threats and determining the purpose of intelligence.
In 1949, Sherman Kent, one of the intellectual architects of U.S. intelligence, published Strategic Intelligence for American World Policy, offering broad yet foundational definitions of intelligence. Yet even Kent recognized the inadequacy of early frameworks. By 1955, he was calling for a comprehensive body of intelligence literature, one that would provide clarity, accuracy, and consensus on essential terms. Despite Kent’s efforts and many contributions since, no single, universally accepted definition emerged for years. In fact, a RAND practitioner-academic workshop in 2005 titled Toward a Theory of Intelligence reported that participants could not reach a consensus on the meaning of intelligence — a deliberate choice for the workshop's agenda, according to the organizers, to encourage open debate. Discussions at the workshop revealed deep divisions over core elements: the role of secrecy, whether intelligence should be state-exclusive, and whether it should be limited to foreign threats alone.
This intellectual evolution is also reflected in the sheer number of definitions that have emerged over time. Scholars Andrew Macpherson and Glenn Hastedt identified 36 distinct definitions of intelligence in practitioner, scholarly, and legal works from 1945 through 2023. This diversity mirrors the dynamic conditions of each era: evolving threat landscapes, shifting power structures, and changing national priorities. Earlier definitions, such as that in the 1948 National Security Council Intelligence Directive No. 3, emphasized “integrated departmental intelligence that covers the broad aspects of national policy and national security.” This phrasing typified the early Cold War mindset. It was vague, bureaucratic, and focused on aggregating intelligence across distinct government silos for policy support. These early formulations assumed threats were primarily foreign, with intelligence serving as knowledge for military men about other nations.
Current definitions, however, reflect a more nuanced understanding of the threat environment. Definitions offered by the DNI and by Macpherson and Hastedt recognize a much broader range of targets, including global issues, cyber threats, and internal dangers directed at people, property, and the nation’s broader interests. Current understanding of intelligence emphasizes process, and the proactive use of intelligence — not collection-for-curiosity’s-sake, but the pursuit of actionable insights into adversaries’ intentions, capabilities, and vulnerabilities. The goal is clear: to inform policy decisions, anticipate outcomes, and secure a strategic advantage.
To some extent, the evolution of intelligence definitions mirrors the structural shift from DCI to DNI leadership, reflecting a pattern of reactive adaptation, gradual reform, and expanding scope. Both developments acknowledge the growing complexity of modern threats and the need for greater collaboration across the intelligence community. Early intelligence, shaped by Cold War thinking, was narrow and vague, but with the emergence of new challenges like terrorism, cyber warfare, and non-state actors, both the meaning of intelligence and its organizational structure were forced to adapt.
Today’s expansive, integrated understanding of intelligence reflects lessons learned through history and the hard-earned realization that defending the nation requires a multifaceted, collaborative, and anticipatory approach. The story of intelligence is not merely one of definitional refinement — it is the story of adapting to a rapidly changing world.
Sources:
Macpherson, Andrew, and Glenn Hastedt. "A New Quantitative Approach to an Old Question." Studies in Intelligence, September 2023. https://www.cia.gov/resources/csi/static/cc27ce9b678dc69d4bdeef410feffa20/Article-New-Approach-to-Old-Question-Sep-2023.pdf.
Treverton, Gregory F., Seth G. Jones, Steven Boraz, and Phillip Lipscy. Toward a Theory of Intelligence: Workshop Report. Santa Monica, CA: RAND Corporation, 2005. https://www.rand.org/pubs/conf_proceedings/CF219.html. Also available at: https://www.rand.org/content/dam/rand/pubs/conf_proceedings/2006/RAND_CF219.pdf.
Best, Richard A. 2014. "Leadership of the U.S. Intelligence Community: From DCI to DNI." International Journal of Intelligence and CounterIntelligence 27 (2): 253–333. https://www.tandfonline.com/doi/full/10.1080/08850607.2014.872533.
Office of the Director of National Intelligence. "What Is Intelligence?" Accessed April 8, 2025. https://www.dni.gov/index.php/what-we-do/what-is-intelligence.