  Observations of quasar absorption systems relevant for studies of star
formation at redshift 2 </= z </= 4 are briefly reviewed. Emphasis is given on
the role played by dust in our understanding of the star formation history of
galaxies detected as absorption systems. Local interstellar studies are used as
a reference for understanding the properties of high redshift interstellar
media. An example is shown of the potential effects of dust extinction on the
metallicity-N(HI) distribution obtained from magnitude-limited surveys of
damped lyman alpha absorbers.
