Jean Lilensten works in ionospheric physics, modelling the electron transport in the planetary upper atmospheres. Jean discovered that the nightglow (including aurora) is polarized, and devotes most of his research to dig through in order to deduce what parameters can be deduced from the polarization parameters. Jean contributed to create the Journal of Space Weather and Space Climate, the space weather and space climate international medals, and the European Space Weather Week (with a full bunch of colleagues and friends). Finally, he was at the origin of the E-SWAN association in order to coordinate Space Weather in Europe.