The small temperature anisotropy and polarization of the cosmic microwave
background (CMB) radiation have been the target of numerous earth-based,
baloon-born and satellite missions in the last two decades.
Upcoming CMB experiments, equipped with higher sensitivity and angular
resolution, will provide us with higher fidelity probes of the CMB
polarization state and second-order effects, such as comptonization of the CMB by
the Sunyaev-Zeldovich (SZ) effect.
The CMB is essentially a snapshot of the universe at recombination and
carries a valuable information about a much earlier process, cosmological
inflation. Secondary effects that took place much later, at
redshifts of a few, such as gravitational lensing of the CMB by the
intervening large scale structure and the SZ effect provide us with
cosmological bounds on neutrino masses and chemical potentials as
well as the dark energy equation-of-state. Rotation of the CMB
polarization-plane, due to non-standard coupling of the electromagnetic
field to other scalar fields, 'cosmological birefringence', can be used to
set limits on the axion mass and coupling to electromagnetic fields.
Finally, spectral distortions in the SZ effect can be used to constrain
non-standard scalings of the CMB temperature with redshift.
