Galactic winds are the primary mechanism by which energy and metals are
recycled in galaxies and are deposited into the intergalactic medium. New
observations are revealing the ubiquity of this process, particularly at high
redshift. We describe the physics behind these winds, discuss the observational
evidence for them in nearby star-forming and active galaxies and in the
high-redshift universe, and consider the implications of energetic winds for
the formation and evolution of galaxies and the intergalactic medium. To
inspire future research, we conclude with a set of observational and
theoretical challenges.Comment: Paper to be published in 2005 Annual Review of Astronomy &
Astrophysics; revision based on comments from readers and production editor.
Figure 1 was replaced to show the proper density scale. A PDF file combining
both text and figures is available at
http://www.astro.umd.edu/~veilleux/pubs/araa.pd
