Cosmic microwave background radiation

The cosmic microwave background radiation (CMBR) is widely interpreted as the thermal afterglow of a hot big bang. Measurements of the CMBR intensity as a function of frequency constrain the history of cosmic energetics. Measurements of the anisotropy in the CMBR temperature provide a snapshot of the distribution of fluctuations in the gravitational potential at the earliest stages of cosmic structure formation. The authors review the interpretation of the CMBR emphasizing the status of current observations and future observational prospects. Our knowledge of the CMBR will dramatically increase in the first decade of the twenty-first century.