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 better angular resolution, will provide us with high fidelity probes of CMB polarization state and secondaries, such as Comptonization of the CMB by the intracluster plasma, the Sunyaev-Zeldovich (SZ) effect.

  The CMB is essentially a snapshot of the universe at recombination and carries valuable information about a much earlier process, cosmological inflation. Secondary effects that took place billions of years 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 other cosmological parameters. 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.