  We review the observational evidences for tidal dwarf galaxies, a class of
small galaxies formed out of the tidal debris of collisions between massive
galaxies. Tidal dwarfs are found far from the interacting parent galaxies,
associated to massive clouds of atomic hydrogen located at the tip of long
tidal tails. These newly formed galaxies are among the best cases for the study
of galaxy formation in the nearby Universe.
