  The launch of the Chandra (NASA) and XMM-Newton (ESA) X-ray observatories in
1999 has revolutionized our view of the Universe, by providing astrophysical
information about many classes of sources with unprecedent detail. The high
throughput of XMM-Newton makes it the ideal instrument to provide low to
moderate resolution spectroscopy of faint and extended sources. After 3 years
of operations, XMM-Newton has observed many types of astronomical sources and
delivered very interesting results in many areas. In this review, we highlight
a few points where the contribution of XMM-Newton has significantly furthered
our knowledge of the energetic Universe.
