K. Subrahmanyam (born 1929) is a prominent international strategic affairs analyst, journalist and former Indian civil servant. Considered a proponent of Real politik, Subrahmanyam has long been an influential voice in Indian security affairs. He is most often referred to as the doyen of India's strategic affairs community, and, more contentiously, as the premier ideological champion of India's nuclear deterrent. Subrahmanyam has been a key figure in framing and influencing Indian security and nuclear policy. And in advocating Indian nuclear positions on the global stage, both as a policy wonk and as a journalist. He is the founding director of the New Delhi-based Institute for Defence Studies and Analyses. He is also noted for having steered several Indian government committees and commissions of inquiry, including one on a war fought between India and Pakistan. Subrahmanyam has lately been a major advocate of the 2007 Indo-US civilian nuclear agreement, adding some heft to the Manmohan Singh government's championing of the deal in the face of much opposition.

Subrahmanyam (born January 1929) grew up in Tiruchirapalli and Madras. Enrolling at Presidency College he received an M.Sc. in Chemistry from Madras University in 1950 and, after standing first in the Civil Services Examination that year, was appointed to the Indian Administrative Service in 1951. After service in the Tamil Nadu cadre and in the Defence Ministry, he was appointed a Rockefeller Fellow in Strategic Studies at the London School of Economics in 1966. On returning to India he was appointed Director of the newly created Institute for Defence Studies and Analyses (IDSA) in New Delhi, a position he held until 1975. He then went on to a number of senior Indian government positions—including Chairman of India's Joint Intelligence Committee in New Delhi, Home Secretary for Tamil Nadu and Union Secretary for Defence Production in the Ministry of Defence—before returning as Director of IDSA in 1980. He returned to England as a Visiting Professor and Nehru Fellow at St. John's College, Cambridge in 1987. Between 1974 and 1986 Subrahmanyam also served on a number of United Nations and other multilateral study groups, on issues such as Indian Ocean affairs, disarmament and nuclear deterrence; and also at various Pugwash conferences as a senior member.

Subrahmanyam is the author or co-author of fourteen books. These include The Liberation War (1972) with Mohammed Ayoob about the Bangladesh Liberation War, Nuclear Myths and Realities (1980), India and the Nuclear Challenge (1986), The Second Cold War (1983) and Superpower Rivalry in the Indian Ocean (1989) with Selig S Harrison.

Subrahmanyam declined the Indian government honour of a Padma Bhushan in 1999, stating that bureaucrats and journalists should not accept government awards.