Physics of accretion flows around compact objects

Several physical and astrophysical problems related to accretion onto black holes and neutron stars are shortly reviewed. I discuss the observed differences between these two types of compact objects in quiescent Soft X-ray Transients. Then I review the status of various non-standard objects suggested as an alternative to black-holes. Finally I present new results and suggestions about the nature of the jet activity in Active Galactic Nuclei. {To cite this article: J.-P. Lasota, C. R. Physique 6 (2006).}