Luminosity bias: from haloes to galaxies
  Large surveys of the local Universe have shown that galaxies with different
intrinsic properties, such as colour, luminosity and morphological type display
a range of clustering amplitudes. Galaxies are therefore not faithful tracers
of the underlying matter distribution. This modulation of galaxy clustering,
called bias, contains information about the physics behind galaxy formation. It
is also a systematic to be overcome before the large-scale structure of the
Universe can be used as a cosmological probe. Two types of approaches have been
developed to model the clustering of galaxies. The first class is empirical and
filters or weights the distribution of dark matter to reproduce the measured
clustering. In the second approach an attempt is made to model the physics
which governs fate of baryons in order to predict the number of galaxies in
dark matter haloes. I will review the development of both approaches and
summarize what we have learnt about galaxy bias.
