HD 40307 is an orange K-type dwarf (about 0.77 solar masses, 4,956 K), 42 light-years from Earth. HD 40307 is a nearby K dwarf with a packed set of super-Earths on short orbits, one of the early rich low-mass systems. The system hosts 5 confirmed planets on orbits ranging from 4.3 days to 198 days. With 5 confirmed worlds, HD 40307 is a densely packed system whose resonances, spacing, and formation history are active research topics. Mutual gravitational tugs between the planets can slowly reshape their orbits, preserving clues to the system's assembly. HD 40307 b skims its star closer than Mercury orbits the Sun. Its low mass makes HD 40307 b a Neptune- or super-Earth-class world rather than a gas giant.