Outphasing is an attractive means of producing radio-frequency signals in applications such as particle accelerators and communications transmitters as it can maintain high efficiency over a wide range of amplitudes. Previously, there was no established method for the design of outphasing systems. The investigation reported here therefore developed a design technique and used it to develop a prototype outphasing system. The prototype amplifier system utilizes existing hardware previously developed for use in an EER system. It operates at 650 MHz and delivers a PEP output of 200 W with an overall efficiency of 77 percent. An overall efficiency of 77 percent or more is maintained over the upper three fourths of the power range. This is the entire dynamic range used in most particle accelerators and a significant part of the amplitude range of most communication signals.