The Klystrode® (IOT) is a new high power electron tube which combines the features of Klystron and the Tetrode. During the past six years it has virtually taken over the UHF-TV market and has demonstrated its capabilities in high power research applications. This paper describes the principles of Klystrode IOT operation and the power and frequency ranges where it is most useful. Field experience with over fifty (50) transmitters in UHF TV service is reported as well as test results from high power scientific devices operated at 267 MHz, 250 kW (CW) and 425 MHz, 500 kW (pulse). Finally, future improvements in the Klystrode IOT to reduce cost, improve efficiency and optimize the tube for industrial applications.