This report discusses the role of monotony in Air Traffic Control (ATC). Despite its obvious relevance as a critical individual state in air traffic controllers, monotony has not been well researched in the past. To describe evoking and contributing factors, distinguish similar critical states such as fatigue and satiation, and define countermeasures, three experimental studies were conducted with a total of 32 air traffic controllers (ATCO) in the simulated and ten ATCOs in an operational air traffic control environment.