The microwave landing system (MLS) is being developed as the next generation approach and landing system to replace the present worldwide instrument landing system (ILS). In order to satisfy diverse users such as civil and military aviation and conventional and V/STOL aircraft, the MLS employs compatible modular configurations. The five-year National MLS Development Program, half over, has just completed a hardware feasibility demonstration phase, is about to choose the best technique, either scanning beam or Doppler scan, and in the next phase will select a single national system from among competing contractors. Meanwhile, the International Civil Aviation Organization has initiated a program directed toward the selection of a new “nonvisual approach and landing system.” The United States is one of five member countries proposing candidates for international standardization. Operational advantages provided by the MLS include far greater flying precision and flexibility, including curved or segmented approaches in three dimensions; and flare guidance for al-lweather automatic landing capability, resulting in greater safety while increasing airport capacities. At the same time, on a compatible basis, the economic and performance needs of general aviation are being satisfied.