  The study of anisotropies in the Cosmic Microwave Background radiation is
progressing at a phenomenal rate, both experimentally and theoretically. These
anisotropies can teach us an enormous amount about the way that fluctuations
were generated and the way they subsequently evolved into the clustered
galaxies which are observed today. In particular, on sub-degree scales the rich
structure in the anisotropy spectrum is the consequence of gravity-driven
acoustic oscillations occurring before the matter in the universe became
neutral. The frozen-in phases of these sound waves imprint a dependence on many
cosmological parameters, that we may be on the verge of extracting.
