How will ballistic missile defences affect nuclear deterrence? This is a question as old as the nuclear revolution but has attained significance in the current security environment wherein nuclear-armed states are increasingly pursuing development and deployment of BMD and their doctrinal integration with strategic forces and postures. Yet, the advent of BMD is bereft of conceptual clarity as their effects on nuclear deterrence is yet to be aptly understood. This article explores the utility of the offence-defence theory to determine whether BMD will inherently remain defensive or could provide a net deterrent value when postured and operated alongside offensive forces.