From HomoExcelsior

A classification of possible civilizations after energy usage.

• Type I civilizations control all available energy on a single planet.
• Type II civilizations control all available energy in a solar system, perhaps using a dyson sphere.
• Type III civilizations control use all available energy in an entire galaxy.

Mitch Porter suggested that a Type IV civilization controls all available energy in the entire universe.

We are currently moving towards a Type I civilization.

See also Drake's Equation and the Fermi Paradox.