This paper describes the construction and operation of an electronic foam controller suitable for use with fermentation vessels. Details are given of a complete foam control system making use of the electronic controller for the control of fermentations of the aerobic type in which large quantities of air are dispersed, and large amounts of electric energy are dissipated. The electronic foam controller operates at low electrode voltage, and is simple and easy to construct. Components are readily available. The controller is actuated when foam in the fermentor touches an insulated electrode, and small increments of antifoam agent are then admitted as permitted by a timer. The controller may be used for other purposes, such as level control, or interface control in liquid-liquid systems. By incorporating several sensing and activating circuits into the controller, it may be used to perform several functions simultaneously.