  It is presented a brief review on gravitational waves (GWs). It is shown how
the wave equation is obtained from Einstein's equations and how many and how
are the polarization modes of these waves. It is discussed the reasons why GWs
sources should be of astrophysical or cosmological origin. Thus, it is
discussed what would be the most likely sources of GWs to be detected by the
detectors of GWs currently in operation and those that should be operational in
the future, emphasizing in particular the sources involving compact objects.
The compact objects such as neutron stars, black holes and binary systems
involving compact stars can be important sources of GWs. Last but not least, it
is discussed the GWs astrophysics that is already possible to do, in particular
involving the compact objects.
