The Kardashev scale, named for Nikolai Kardashev, is way to measure a civilization's technological progress with energy use as a metric. In its original form, it has three discrete but progressive levels:
- A Type I civilization, a planetary civilization, can use and store all of the energy available on its planet.
- A Type II civilization, a stellar civilization, can use and control energy at the scale of its planetary system.
- A Type III civilization, a galactic civilization, can control energy at the scale of its entire host galaxy.
One of the methods most influential proponents, Carl Sagan, suggested a continuum of levels from K0.0 to K4.0 (universal civilization).