The Kármán line (or von Kármán line ) is a proposed conventional boundary between Earth's atmosphere and outer space set by the international record-keeping body FAI (Fédération aéronautique internationale) at an altitude of 100 kilometres (54 nautical miles; 62 miles; 330,000 feet) above mean sea level. However, such definition of the edge of space is not universally adopted.

The Kármán line has no particular physical meaning, in that there is no noticeable change in the characteristics of the atmosphere across it, but is important for legal and regulatory purposes, since aircraft and spacecraft are subject to different jurisdictions and legislations. International law does not define the edge of space, or the limit of national airspace.

The line lies well above the altitude reachable by a conventional airplane or a high-altitude balloon, and is approximately where satellites, even on very eccentric trajectories, will decay before completing a single orbit.

While experts disagree on exactly where the atmosphere ends and space begins, most regulatory agencies (including the United Nations) accept the FAI's Kármán line definition or something close to it. As defined by the FAI, the Kármán line was established in the 1960s. Various countries and entities define space's boundary differently for various purposes.

The Kármán line is named for Theodore von Kármán (1881–1963), a Hungarian-American engineer and physicist who was active in aeronautics and astronautics. In 1957, he was the first person to attempt to calculate a theoretical limit of altitude for airplane flight.