  The High Energy Stereoscopic System (H.E.S.S.) is a southern hemisphere array
of four Imaging Atmospheric Cherenkov Telescopes observing the sky in the very
high energy gamma-ray range (E $>$ 100 GeV). VHE observations are an invaluable
tool to study the acceleration and propagation of energetic particles in many
astrophysical systems where relativistic outflows are the main drivers of the
emission, such as AGNs and galactic binary systems. In this paper the main
results of the H.E.S.S. observations of these objects will be reviewed, and the
general picture that emerges from them will be presented. We will also comment
on prospects for future investigations with H.E.S.S.-II.
