  This paper given at the Strasbourg NATO school on the CMB and cosmology
reports the contents of four hours of lectures on the CMB spectrum, potential
distortions, and implications. It was followed by 6 hours of lectures on CMB
anisotropy. This paper reviews the observations and theoretical implications
for the CMB frequency spectrum - both for the monopole (essentially total
power) and the dipole and higher order anisotropies including the
Sunyaev-Zeldovich effect.
