We describe simple interferometric reflectometry systems that have been applied to real-time monitoring of epitaxial growth in a variety of crystal growth systems. These include molecular beam epitaxy (MBE) systems from Vacuum Generators and Varian, and metalorganic chemical vapor deposition reactors from Aixtron and Emcore. The reflectometry systems are composed entirely of off-the-shelf hardware, including charge-coupled-device-based spectrometers and light bulb white light sources. These fixed modules are connected by simple fiber optic links. Input and output lenses are matched to the crystal growth systems such that unmodified viewports and rotating sample stages/platens are fully accommodated. The systems are driven by a Windows(TM)-based program operating on a conventional PC. This program permits display of the time-dependent spectra as either line graphs or grayscale converted "fingerprints" that may be overlaid, in real time, on data from reference growth runs. It also includes provision for full simulation of complex layered structures in the GeSi, AlGaAs, and InGaAsP materials systems, along with corrections for elevated growth temperature. For the MBE-based GeSi system, vertical resonant cavity photodiode structures were monitored. The reflectometry system easily revealed growth rate deviations of less than 1% and permitted termination of growth at precise resonance conditions.