By construction, optical (and near-infrared) interferometers typically have resolutions designed to resolve stellar and circumstellar features. Therefore gaging the point-source response of the interferometer in its operating environment is critical to the scientific interpretation of data from these devices. This is typically performed with observations of calibration sources that are modeled to be simple and quasi-unresolved by the interferometer. Herein I will discuss the goals and strategies for and issues with the selection of objects to serve as calibration sources for optical interferometry visibility measurements.