  There is wide consensus that galaxy outflows are one of the most important
processes determining the evolution of galaxies through cosmic time, for
example playing a key role in shaping the galaxy mass function. Our
understanding of outflows and their drivers, however, is in its infancy ---
this is particularly true for the cold (neutral atomic and molecular) phases of
outflows, which present observational and modeling challenges. Here we outline
several key open questions, briefly discussing the requirements of the
observations necessary to make progress, and the relevance of several existing
and planned facilities. It is clear that galaxy outflows, and particularly cold
outflows, will remain a topic of active research for the next decade and
beyond.
