  We summarize the theoretical and observational status of the study of the
Cosmic Microwave Background radiation. Its thermodynamic spectrum is a robust
prediction of the Hot Big Bang cosmology and has been confirmed
observationally. There are now 76 observations of Cosmic Microwave Background
anisotropy, which we present in a table with references. We discuss the
theoretical origins of these anisotropies and explain the standard jargon
associated with their observation.
