  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).}
