  I review the basic theory of the cosmic microwave background anisotropies in
adiabatic cold dark matter cosmologies. The latest observational results on the
CMB power spectrum are consistent with the simplest inflationary models and
indicate that the Universe is close to spatially flat with a nearly scale
invariant fluctuation spectrum. We are also beginning to see interesting
constraints on the density of CDM, with a best fit value of omega_c = Omega_c
h^2 of about 0.1. The CMB constraints, when combined with observations of
distant Type Ia supernovae, are converging on a Lambda-dominated Universe with
Omega_m approx 0.3 and Omega_Lambda approx 0.7.
