Cosmic Microwave Background Anisotropy experiments have recently resolved sub-horizon structures on the last scattering surface at redshift 1000, with high
signal-to-noise ratio. The power spectrum of the detected anisotropy is consistent with the simplest inflationary scenario and with the physics of the primeval plasma. I
review the technical advances, which made this possible, the current results and their cosmological significance, with special attention to the determination of the total
mass-energy in the Universe.
* Tea & coffee will be served at 16.00 hrs.