  The measurements of COBE/FIRAS have shown that the CMB spectrum is extremely
close to a perfect blackbody. There are, however, a number of processes in the
early Universe that should create spectral distortions at a level which is
within reach of present day technology. In this talk, I will give a brief
overview of recent theoretical and experimental developments, explaining why
future measurements of the CMB spectrum will open up an unexplored window to
early-universe and particle physics with possible non-standard surprises but
also several guaranteed signals awaiting us.
