  I discuss the properties of gas-rich forming galaxies. I particularly
emphasize the latest results on Lyman alpha emission that are relevant to the
search of distant young galaxies. The interdependance of the Lyman alpha escape
with the properties of the ISM in starburst galaxies is outlined. A new model
from G. Tenorio-Tagle and his collaborators explaining Lyman alpha profiles in
starburst galaxies from the hydrodynamics of superbubbles powered by massive
stars is presented. I stress again that since Lyman alpha is primarely a
diagnostic of the ISM, it is mandatory to understand how the ISM and Lyman
alpha are related to firmly relate Lyman alpha to the cosmic star-formation
rate.
