Expressions for the temperature coefficients of longitudinal and shear modes of vibrations are derived and discussed. The conditions for zero temperature coefficients are stated. In the case of the shear modes of vibration, the orientations which permit zero temperature coefficients are a function of the overtones and of the crystal dimensions. Hence, no unique angle of orientation independent of the dimensions of the specimen exists. The theory is applied to the grinding of quartz plates which shall regularly have temperature coefficients lower than those obtained by previous methods of orienting these plates.