  The 8m class telescopes in the ground-based optical astronomy together with
help from the ultra-sharp eye of the Hubble Space Telescope have enabled us to
observe forming galaxies beyond redshift $z=5$. In particular, more than twenty
Ly$\alpha$-emitting galaxies have already been found at $z > 5$. These findings
provide us with useful hints to investigate how galaxies formed and then
evolved in the early universe. Further, detailed analysis of Ly$\alpha$
emission line profiles are useful in exploring the nature of the intergalactic
medium because the trailing edge of cosmic reionization could be close to $z
\sim 6$ -- 7, at which forming galaxies have been found recently. We also
discuss the importance of superwinds from forming galaxies at high redshift,
which has an intimate relationship between galaxies and the intergalactic
medium. We then give a review of early cosmic star formation history based on
recent progress in searching for Ly$\alpha$-emitting young galaxies beyond
redshift 5.
