This paper describes a Radio Frequency (RF) plasma ignitor concept intended for application to internal combustion engines. This system features a high Q quarter-wave coaxial cavity resonator, of simple construction, serving as a tuning element in the RF power supply, a voltage magnifier, and a discharge device attached to the combustion chamber. The resonator is filled with a dielectric and open at the discharge end. The center conductor is terminated with a revolute solid capacitive electrode which concentrates the associated electric field. This non-uniform electric field within the air/fuel mixture creates a corona discharge plasma which is excited at the RF operating frequency and the resulting ionic species recombine to initiate combustion. The RF excitation, relative to DC, reduces breakdown voltage and electrode degradation. Resonators sized to physically replace existing spark plugs will operate at about 2 GHz, and for typical ignition timing, must ignite mixtures at pressures as high as 10 atm. Tests of a 200 MHz system at 1 atmosphere show that the RF cavity feed configuration and the shape and location of the capacitive electrode are critical factors affecting performance and efficiency.