  Various observational techniques have been used to survey galaxies and AGN,
from X-rays to radio frequencies, both photometric and spectroscopic. I will
review these techniques aimed at the study of galaxy evolution and of the role
of AGNs and star formation as the two main energy production mechanisms. I will
then present as a new observational approach the far-IR spectroscopic surveys
that could be done with planned astronomical facilities of the next future,
such as SPICA from the space and CCAT from the ground.
