  The detailed spectral and spatial characteristics of the signature imprinted
on the cosmic microwave background (CMB) radiation by Compton scattering of the
radiation by electrons in the hot gas in clusters of galaxies - the
Sunyaev-Zeldovich (S-Z) effect - are of great astrophysical and cosmological
significance. In recent years observations of the effect have improved
tremendously; high signal-to-noise images of the effect (at low microwave
frequencies) can now be obtained by interferometric arrays. In the near future,
high frequency measurements of the effect will be made with ground based and
balloon-borne telescopes equipped with bolometeric arrays. Towards the end of
the decade the PLANCK satellite will carry out an extensive S-Z survey over a
wide frequency range. Along with the improved observational capabilities, the
theoretical description of the effect, and its use as a precise cosmological
probe, have been considerably advanced. In this review, I briefly discuss the
nature and significance of the effect, its exact theoretical description, the
current observational status, and prospects for the near future.
