  We study the observed evolution of galaxy clustering as a function of
redshift. We find that the clustering of galaxies decreases as we go from
observations of the local Universe to $z \sim 2$. On the other hand, clustering
of the Lyman break galaxies at $z \sim 3$ is very strong, comparable to the
clustering of present day galaxies. However there are three major factors to
take into account while comparing clustering measurements coming from various
surveys: the so-called ``scale-dependence'' effect, due to measurements being
made at different scales; the ``type-selection'' effect introduced by the fact
that different galaxy surveys select different populations which do not have
the same clustering amplitudes; and the Malmquist bias. We correct for the
first two effects and discuss the implications of Malmquist bias on the
interpretation of the data at different $z$. Then we compare the observed
galaxy clustering with models for the evolution of clustering in some fixed
cosmologies. Correcting for the scale-dependence effect significantly reduces
the discrepancies amongst different measurements. We interpret the observed
clustering signal at high redshift as coming from objects which are highly
biased with respect to the underlying distribution of mass; this is not the
case for $z\simlt 2$ where measurements are compatible with the assumption of a
much lower biasing level which only shows a weak dependence on $z$. Finally we
propose a model-independent test that can be used to place a lower limit on the
density parameter $\Omega_0$.
