Marin County Airport or Gnoss Field (IATA: NOT, ICAO: KDVO, FAA LID: DVO), formerly O56, is a public airport two miles northeast of Novato, California, United States. It covers 90 acres (360,000 m2), and has one runway and one helipad.

Most U.S. airports use the same three-letter location identifier for the FAA and IATA, but Marin County Airport/Gnoss Field is DVO to the FAA and NOT to the IATA (which assigned DVO to Francisco Bangoy International Airport in Davao City, Philippines).

A plan was unveiled in 2014 to extend the length of Gnoss' runway by 1100', to 4400'. The FAA's final recommendation in 2016 called for a 300-foot extension, which would make Runway 31/13 3600 feet. Public commentary, especially from aviators, was negative. Many pilots contended that the FAA has underestimated the level of activity at Gnoss Field.