Galaxies often show enormous outpouring of gas. These ‘galactic winds’ are the result of a collective astrophysical phenomenon in which individual violent events, such as supernovae, join forces to produce spectacular effects. These outflows may hold the clues to several phenomena in astrophysics and cosmology, such as the regulation of star formation in galaxies, or the enrichment of the intergalactic medium with heavy elements. However, the physical processes that drive these outflows are not yet well understood. I will discuss some of these processes that can be important, and how observations can help us constrain the physical model.