During the last twenty years observational cosmology has made enormous progress. One of the main drivers of this progress have been measurements of the fluctuations in the cosmic microwave background (CMB).

In my course I shall first give a introduction to cosmology (the history of the cosmic evolution and its main events: recombination, nucleosynthesis, decoupling of neutrinos, inflation).

Then I shall discuss the fluctuations and polarization of the cosmic microwave background and explain why this is an ideal observational tool to determine cosmological parameters. I shall also discuss 'degeneracies', namely parameter combinations to which CMB anisotropies are insensitive.