The charged particle oscillator is a device by means of which particles of one sign are confined to a limited volume solely by means of a static electric field. In one form it consists of a pair of positively charged wires surrounded by an earthed conducting cylinder. An electron released from rest within the cylinder follows a stable oscillatory path which always passes between the wires and which is up to 5 km in length. The properties of this device have been explored by experiment and by computation, and are discussed with particular reference to its use as a uhv gauge of high sensitivity and as a low pressure ion source.