The Indium Phosphide (InP) Gunn device is fast becoming a key component in the millimeter wave region. The device has superior performance as wideband low noise amplifier, low noise local oscillator, self-oscillating mixer, and low to medium power source. Its development and advances are primarily fueled by military systems requirements and developments covering missile and projectile guidance, high resolution radar systems, intercept secure communications and Eli and ECM functions. In this paper an overview of the current status of indium phosphide Gunn device development and future trends is presented. Covered will be in particular key parameters leading to indium phosphide's advantage at millimeter-wave frequencies, recent material and device developments, oscillators, amplifiers and systems applications with emphasis on current capabilities. Other devices such as InP FET and InP IMPATT devices are not considered in this paper because of their current limitations to microwave frequencies.