I will discuss the nature of the ISM in distant (z~1-6) galaxies and
the evidence for both a high efficiency of star- formation and the
possibility that the IMF is weighted towards massive stars.  The
dominant mechanism regulating both the star formation and the
properties of the ISM is the turbulence generated and the feedback
from the formation of massive stars with a role played by the
classical instabilities of the gas (i.e., a Toomre like instability).
I will emphasize the critical role played by feedback from the
star-formation ISM, in limiting the star-formation intensity, and for
enriching the IGM.