This overview talk will focus on the origin, physical properties, composition, and radiation-induced chemistry of water ice in the interstellar medium, and its connection to comets and other ices in our Solar System. In the Astrochemistry Laboratory at NASA Ames (http://web99.arc.nasa.gov/~astrochem/) we reproduce such ices in the lab and perform spectroscopy and experiments. Understanding the physical characteristics and chemistry of water ices is important for explaining spectroscopic observations of the interstellar medium, and the behavior of comets. Furthermore, ice photochemistry results in the formation of complex organic molecules, of the kind in delivered to Earth by meteorites and comet and asteroidal dust and similar to those seen in living systems. Thus it has been suggested that interstellar ice photochemistry may have played a role in the rise of life on Earth.