K2-18b, also known as EPIC 201912552 b, is an exoplanet orbiting the red dwarf K2-18, located 124 light-years (38 pc) away from Earth. The planet, initially discovered through the Kepler space telescope, is about eight times the mass of Earth, and thus is classified as a super Earth. It has a 33-day orbit within the star's habitable zone.

In 2019, two independent research studies, combining data from the Kepler space telescope, the Spitzer Space Telescope, and the Hubble Space Telescope, concluded that there are significant amounts of water vapor in its atmosphere, a first for a planet in the habitable zone.