The design of a State-of the-Art Infrared Sensor requires a number of diverse disciplines. Without proper programmatic controls, the attendant subsystem design studies can result in the imposition of incompatible requirements on the overall sensor design. One approach for assuring the orderly development of a sensor design is the use of a Sensor Specification which reduces the top level system requirements into a set of self-consistent subsystem requirements. A methodology for generating such a specification is described in this paper. Emphasis is placed on sensors designed for Ballistic Missile Defense (BMD) applications; however, a similar approach can be utilized for any infrared system.