This lecture reviews in simple terms the general subject of large scale magnetic field coupling to plasma flowsin the vicinity of accreting compact stars. The relevant astrophysical phenomenology is summarized.Disk interaction with the magnetosphere ofaccreting stars is first discussed, in particularthe structure of the magnetopause, its stabilityand plasma ejection in so-called propeller systems. The physics of accretion/ejection is then considered. Acceleration and focusing mechanisms ofjets from accretion disks around compact stars or black holes and the question of the self-consistency of accretion and ejection are described. By contrast, small scale MHD turbulence in disks is not discussed, neither are accretion columns near thepolar caps of neutron stars or white dwarfs. The reader is only assumed to have some basic knowledge ofastrophysics and of fluid mechanics and electromagnetism.