Catalogues of galaxies, clusters of galaxies and superclusters - sources of
information to study the large-scale structure of the Universe are reviewed.
The power spectrum of density perturbations, and the correlation function are
discussed as principal description functions which characterize the large-scale
structure. Special attention is payd to the geometric interpretation of these
functions, i.e. the way in which the various properties of the distribution of
galaxies in systems and systems themselves are reflected in these functions. We
discuss cosmological parameters which characterize general properties of the
Universe: the Hubble constant, densities of various populations of the
Universe, and parameters of the power spectrum of galaxies and matter.Comment: LaTex (sty files added), 24 pages, 8 PostScript figures embedded, in
``Understanding the Universe at the close of XXth Century'', ed. M. Signore,
Elseview (in press
