Extremely high frequency is the highest radio frequency band. EHF runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered to be low (or far) infrared light. This band has a wavelength of one to ten millimetres, giving it the name millimeter band.

Radio signals in this band are extremely prone to atmospheric attenuation, making them of very little use over long distances. Even over relatively short distances, rain fade is a serious problem, caused when absorption by rain reduces signal strength.

This band is commonly used in radio astronomy.

In the USA, the band 38.6 - 40.0 GHz is used for licensed high-speed microwave data links, and the 60 GHz band can be used for unlicensed short range (1.7 km) data links with data throughputs up to 2.5 Gbit/s (gigabits per second).