An IOT is a beam driven vacuum electronic RF amplifier. This document represents a comparative overview of the Inductive Output Tube (IOT). Starting with an overview of the IOT, we progress to a comparative discussion of the IOT relative to other RF amplifiers, discussing the advantages and limitations within the frame work of the RF amplifier requirements for the ESS. A discussion on the current state of the art in IOTs is presented along with the status of research programmes to develop 352MHz and 704MHz IOT’s.