Infrared (IR) sensors are critical to all phases of ballistic missile defense (BMD), including surveillance, threat detection, tracking, identification, discrimination, targeting, and interception. The Discriminating Interceptor Technology Program (DITP) under development by the BMDO Sensors and Interceptors Directorate (BMDO/TOS) supports the requirements of BMDO's National Missile Defense and Theater Missile Defense to counter the emerging threat. Focal plane arrays (FPAs) with high sensitivity, high uniformity, large format, flexible wavelength ranges from mid-wave IR (MWIR) to very long wave IR (VLWIR), and multicolor capabilities are required. The effort is also toward FPAs with high reproducibility, high yield, low cost, and manufacturability. The two most promising near-term IR technologies to meet the BMD requirement are mercury cadmium telluride (MCT) photodiodes and quantum well infrared photodetectors (QWIPs). This paper discusses applications and relative merits of both of these detectors in BMDO applications.