Simulations of galaxy formation require strong feedback to produce realistic galaxies. Observations of starburst galaxies both at low and high redshift often show signatures of strong galaxy-wide winds. Are such winds common, and are they the mechanism which pollutes the intergalactic medium with metals? Which are the sources of ionising photons at higher redshift? Detailed observations of galaxies and their surroundings and comparison with cosmological simulations to eliminate biases and test models are required to address these questions.