In this work, in situ cathodoluminescence (CL) is presented as a technique to optimize the molecular beam epitaxy (MBE) growth conditions for InGaN films and structures. InGaN was grown at 1 mu m/h using a reactive nitrogen rf plasma source at substrate temperatures ranging from 550 to 650 degrees C. The quick determination of the emission wavelength and quality from the peak position and width allowed various growth conditions and structures to be tried without removal of the sample from the MBE system. CL scans are presented from samples grown under varying Ga/In flux ratios, III/nitrogen flux ratios, and substrate temperatures showing the usefulness of in situ monitoring for MBE InGaN growth.