We describe a novel second harmonic generation (SHG) microscope that employs heterodyne detection by interfering the epi directed SHG from a sample with SHG from a reference crystal. In addition, the microscope provides complementary reflectance information based on optical coherence microscopy (OCM). The instrument features dual balanced detection to minimize the effect of source fluctuations, and polarization-sensitive detection to measure the nonlinear susceptibility of the sample. Interferometric detection can potentially improve the sensitivity and thus extend the imaging depth as compared with direct detection of SHG.