Microwave background astronomy has arrived. Largely because of improvements in receivers, the last three years have seen the emergence of agreement concerning important measurements of the microwave background radiation (MBR):

– hard evidence that the MBR has a black-body spectrum (see Smoot in these proceedings);

– the unambiguous detection of the Sunyaev-Zeldovich decrement in clusters of galaxies (Birkinshaw et al 1984), and indeed profiles of the decrement across clusters (Birkinshaw in these proceedings);

– the lack of anisotropy in the MBR temperature T on scales of a few arcmin down to ΔT/T˜5×10-5 (Uson & Wilkinson 1984; Readhead, private communication) and the consequent elimination of simple theories of adiabatic primordial fluctuations.