  Since its original formulation the Sunyaev-Zeldovich (SZ) effect has been
recognized as a ``powerful laboratory'' for our comprehension of physical
processes in cosmic structures and to derive crucial information on some
general properties of the universe. After a discussion of the fundamental
concepts and of some well established applications of the SZ effect towards
galaxy clusters, I will focus on dedicated themes related to the SZ effect and
other features in the cosmic microwave background (CMB) of particular interest
in the view of the extremely high angular resolution observations achievable in
the future with the Square Kilometre Array (SKA). SKA will allow the mapping of
the thermal and density structure of clusters of galaxies at radio and
centimetre bands with unprecedented resolution and sensitivity and with an
extremely accurate control of extragalactic radio source contamination. The
signatures from SZ effects and free-free emission at galactic scales and in the
intergalactic medium probe the structure evolution at various cosmic times. The
detection of these sources and their imaging at the high resolution and
sensitivity achievable with SKA will greatly contribute to the comprehension of
crucial cosmological and astrophysical aspects, as the physical conditions of
early ionized halos, quasars and proto-galactic gas. The spectacular
improvement in our understanding of the properties of extragalactic radio
sources at very faint fluxes achievable with SKA will allow to accurately model
their contribution to the diffuse radio background, greatly contributing to the
interpretation of next generation of CMB spectrum experiments devoted to probe
the thermal plasma history at early times.
