Inhomogeneous broadening of a dilute chromophore’s optical transition can provide detailed information about disorder in crystalline systems. Certain nonlinear experiments such as fluorescence and phosphorescence line narrowing and spectral hole burning, which probe the correlation between the inhomogeneous frequency distributions of two different transitions, are capable of yielding even more information. In this paper we present a microscopic lattice theory of inhomogeneous broadening by point defects, focusing specifically on the correlation between a pair of transitions. We develop a series of approximations for the joint frequency distribution for the two transitions that are valid for all possible defect densities, and which are shown to be accurate in comparison with exact numerical calculation. The model is capable of describing frequency distributions with any amount of correlation. We discuss several experiments within the context of this theory.