A stellar interferometer is a singularly complex instrument and its design and implementation involve numerous technical sub-disciplines. However, a person or group of people needs to understand the overall purpose, requirements and constraints of a proposed interferometer well enough to develop a conceptual design, perform preliminary instrument/payload system engineering and identify critical need areas before the detailed design and implementation processes can begin. Also, as design and development of the interferometer get underway, interferometer models and testbeds must be constructed and exercised to explore and validate instrument- and component-level concepts. It is in this sense that Stellar Interferometry is an overarching discipline.