Because faint, low mass galaxies are numerous at high redshifts, their impact on the Universe is expected to be significant. They may host a substantial fraction of the Universe's star formation, provide many of the energetic photons needed to reionize the hydrogen gas surrounding galaxies, and affect their surroundings via powerful, starburst-driven galactic outflows of gas. I will discuss a variety of observations aimed at characterizing the physical conditions in low mass galaxies during the peak epoch of star formation, when the Universe was ~20% of its current age, with particular emphasis on the characterization of the gas surrounding galaxies.
