The purpose of this thesis is to give an account of the comparable use of dissonance of Palestrina, Lassus, and Victoria through harmonic analysis and statistical comparison, illustrating the stylistic differences among the three composers works. The thesis does. not attempt to cover text setting, melodic construction, ranges, or aesthetic evaluation of composition other than that which pertains to dissonance. The analysis of dissonance was done with primary consideration being given to the vertical structure of the harmony, observing the linear structure only with relation to the approach and resolution of that dissonance.