This school, the 6th session in a series organized at l'Ecole de Physique des Houches since 2011, is intended as a doctoral training program on plasma physics. It will cover the basics of the theory and simulation of plasmas. Space, astrophysical as well as laboratory plasmas will be considered with a special emphasis on the timely topic of plasmas under extreme conditions as found e.g. in the interior of planets, in the most violent astrophysical environments, or created using extreme-light lasers.