A modular polarization spectrometry system for the measurement of the degree of polarization (linear or circular) of luminescence intensity is described. It is based on polarization modulation with a photoelastic modulator and two lock‐in amplifiers for signal recovery. Interfaced to the spectrometer is a microcomputer configured with CRT monitor, disk drive, and digital printer to provide system control and to permit digital data storage and data manipulations such as multiple scan averaging and averaged background subtraction. The system described is capable of measuring linearly polarized emission, linearly polarized excitation luminescence, and circularly polarized emission spectra. The modular design also allows the spectrometer to be rapidly and easily modified for the measurement of circular dichroism, magnetic circular dichroism, or magnetic circularly polarized emission. The system performance is demonstrated.