Abstract: 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 global star formation, provide many of the energetic photons needed to reionize the universe, and contribute to the enrichment of the intergalactic medium through the expulsion of metals in galactic outflows. Because of their faintness, however, the properties of these galaxies are difficult to determine. I will discuss a variety of observations aimed at characterizing the physical conditions in low mass galaxies at redshifts z~2-3, the peak epoch of star formation in the Universe, with particular emphasis on the study of galactic outflows in faint galaxies.