Infrared (IR) sensors and focal plane arrays (FPAs) are widely used in ballistic missile defense (BMD) for surveillance, target detection, target tracking, and discrimination. These functions are performed from satellites, aircraft platforms, fixed locations or interceptors. The temperatures of most advanced BMD targets require FPA wavelengths in the mid-wave IR, long-wave IR, or very-long-wave IR bands. Important FPA characteristics for future BMD FPAs will include large format, high sensitivity, low 1/f noise, good uniformity, and high operability. Due to the colder environment in space applications, very-long-wave IR is very important for sensor design. IR sensors with high performance at low temperature and very-long-wave is especially important for IR space systems. In addition, multicolor IR sensing is important to eliminate the effects of earthshine in exoatmospheric discrimination. In this paper, an overview of the state-of-the-art of IR sensors will be given, and the advantages and shortfalls of each IR material system for BMD and space-based applications will be discussed.