Kepler-603 is a Sun-like G-type star (about 1.01 solar masses, 5,808 K, 1.01 solar radii), 1,540 light-years from Earth. Kepler-603 d is a planet with 1.3 Earth radii, with an orbital period of 6.2 days, discovered in 2016 via transit. Kepler-603 b is a planet with 2.6 Earth radii, with an orbital period of 21.1 days, discovered in 2016 via transit. Kepler-603 c is a planet with 6.5 Earth radii, with an orbital period of 128 days, discovered in 2016 via transit. Mutual gravitational tugs between the planets can slowly reshape their orbits, preserving clues to the system's assembly.