In this lecture I review the theory of magnetized accretion discs driving jets, with a focus on Young Stellar Objects (YSOs). I first introduce observational and theoretical arguments in favor of the “disc wind” paradigm. There, accretion and ejection are interdependent, requiring therefore to revisit the standard picture of accretion discs. A simple magnetostatic approach is shown to already p...

We present stationary models of protostellar population  (Pop , for short) accretion discs, compare them to Pop  discs, and investigate the influence of the different chemical compositions on the occurence of gravitational, thermal and thermal-viscous instabilities in the discs. In particular in the cooler regions, we find major differences between Pop  and Pop  discs, both in the st...

Context. Keplerian accretion discs around massive black holes (MBHs) are gravitationally unstable beyond a few hundredths of parsec and should collapse to form stars. It was indeed shown recently that an accretion/star formation episode took place a few millions years ago in the Galactic Center (GC). This raises the question of how the disc can survive in AGN and quasars and continue to transpo...

The low frequency radio luminosity is believed to be an indicator of jet power, while the optical/UV emission is probably from accretion discs in the nuclei of steep-spectrum radio quasars. We present a correlation between the ratio of radio to optical luminosities and the continuum spectral index in blue/UV bands, which might indicate that the continuum shape in blue/UV bands is related to the...

Accretion in the nuclei of active galaxies may occur chaotically. This can produce accretion discs which are counter–rotating or strongly misaligned with respect to the spin of the central supermassive black hole (SMBH), or the axis of a close SMBH binary. Accordingly we consider the cancellation of angular momentum in accretion discs with a significant change of plane (tilt) between inner and ...