This Note illustrates how a confocal microscope may be modified to conduct Rayleigh-Brillouin mapping experiments that yield very useful information on the mechanical properties of interfacial materials in small volume elements. While the modifications to the microscope are quite straightforward, they do entail significant changes in the optical design. The instrument described herein consists of an argon ion laser equipped with an actively stabilized intercavity étalon that serves as the excitation source for a modified Zeiss LSM 310 confocal laser scan microscope. The optics of the microscope were reconfigured to enable interfacing of the microscope with a tandem triple-pass Fabry-Pérot interferometer. This instrument enables three-dimensional Rayleigh-Brillouin spectral mapping of samples at micron spatial resolution. The performance of the instrument and its ability to perform both lateral and depth scans of the acoustic phononvelocity and, hence, the longitudinal modulus across bonded polymer/polymer and polymer/ceramic interfaces are illustrated and discussed.