  Polarization induced by cosmological scalar perturbations leads to a typical
anisotropy pattern, which can best be analyzed in Fourier domain. This allows
one to unambiguously distinguish cosmological signal of polarization from other
foregrounds and systematics, as well as from polarization induced by non-scalar
perturbations. The precision with which polarization and cross-correlation
power spectra can be determined is limited by cosmic variance, noise and
foreground residuals. Choice of estimator can significantly improve our
capability of extracting cosmological signal and in the noise dominated limit
the optimal power spectrum estimator reduces the variance by a factor of two
compared to the simplest estimator. If foreground residuals are important then
a different estimator can be used, which eliminates systematic effects from
foregrounds so that no further foreground subtraction is needed. A particular
combination of Stokes $Q$ and $U$ parameters vanishes for scalar induced
polarization, thereby allowing an unambiguous determination of tensor modes.
Theoretical predictions of polarization in standard models show that one
typically expects a signal at the level of 5-10$\mu$K on small angular scales
and around 1$\mu$K on large scales ($l<200$). Satellite missions should be able
to reach sensitivities needed for an unambiguous detection of polarization,
which would help to break the degeneracies in the determination of some of the
cosmological parameters.
