London, named after the physicist Fritz London, is a quantum chemistry program that was written to be a unique tool to explore molecules in magnetic fields. The standard quantum chemical technique is a two-step process, where the system is first modelled in the absence of a magnetic field, and then effects of a weak magnetic field are added as small correction terms. (A technique known as perturbation theory.) By contrast, London models the magnetic field effects directly. As a result, London can be used to explore effects from weak as well as strong magnetic fields. Some of the most interesting effects in fact occur for magnetic fields that are far beyond present-day laboratory experiments, but which can be generated around white dwarf stars.