Kepler-166 is a Sun-like G-type star (about 0.88 solar masses, 5,350 K, 0.83 solar radii), 604 light-years from Earth. Kepler-166 b is a planet with 2.3 Earth radii, with an orbital period of 7.7 days, at 0.072 AU from its star, discovered in 2014 via transit. Kepler-166 c is a planet with 2.4 Earth radii, with an orbital period of 34.3 days, at 0.195 AU from its star, discovered in 2014 via transit. Kepler-166 d is a planet with 1.7 Earth radii, with an orbital period of 1.6 days, discovered in 2016 via transit.