  Galaxy evolution depends strongly on the environment. Dynamical interactions
and subsequent evolution make galaxies more concentrated, with higher surface
densities, and also trigger star-formation, which consumes the available cold
gas. Already at z=0, a large variety of galaxy types are observed, with
different evolution stages, from the unevolved gas rich dwarf irregulars, or
low surface brightness galaxies, to early-type concentrated galaxies, with no
remaining gas.
  The dynamical processes of galaxy interactions, including internal evolution,
are reviewed and evidence is shown of much larger interaction/merging rate at
high redshift.
