  Observational tests for the Cosmological Principle are reviewed. Assuming the
FRW metric we then summarize estimates of cosmological parameters from various
data sets, in particular the Cosmic Microwave Background and the 2dF galaxy
redshift survey. These and other analyses suggest a best-fit Lambda-Cold Dark
Matter model with Omega_m = 1 - Omega_lambda = 0.3 and H_0 = 70 km/sec/Mpc. It
is remarkable that different measurements converge to this `concordance model',
although it remains to be seen if the two main components of this model, the
dark matter and the dark energy, are real entities or just `epicycles'. We
point out some open questions related to this fashionable model.
