Airspace today is densely penetrated by Wi-Fi networks, GPS services, and broadcasting and mobile phone signals. This process, what we call the mediatization of the air, is not so new, as it began in the first two decades of the 20th century, with the advent of wireless telegraphy. Based on archival research, this paper shows that wireless telegraphy mediatized the air and made it a matter of common interest for formerly-disconnected international realms. The mediatized air transformed meteorology, timekeeping, mobility, and transportation, and challenged governance over aerial borders. Overall, this historical study contributes to a different narrative about mediatization by including an invisible and understudied phenomenon that today represents a basic and taken-for-granted infrastructure for global communication.