The principles of quartz resonator operation are reviewed. Particular emphasis is placed on resonant frequency shifts induced by changes in ambient temperature and in the areal mass density, and the lateral stress of thin films on the resonator surfaces. The fact that these three effects depend upon the crystallographic cut of the quartz resonator plate is exploited in developing one−, two−, and three−resonator configurations to measure thin film lateral stress, thin film mass areal density, and/or temperature simultaneously in vacuum. Examples are presented for simultaneous stress and mass measurements for a variety of experimental situations. Additional areas for application of the multiple resonator principle are proposed.