  We use Cosmic Microwave Background (CMB) observations together with the
Red-sequence Cluster Survey (RCS) weak lensing results to derive constraints on
a range of cosmological parameters. This particular choice of observations is
motivated by their robust physical interpretation and complementarity. Our
combined analysis, including a weak nucleosynthesis constraint, yields accurate
determinations of a number of parameters including the amplitude of
fluctuations sigma_8 = 0.89+/-0.05 and matter density Omega_m =0.30+/-0.03. We
also find a value for the Hubble parameter of H_0 =70+/-3km/s/Mpc, in good
agreement with the Hubble Space Telescope (HST) key--project result. We
conclude that the combination of CMB and weak lensing data provides some of the
most powerful constraints available in cosmology today.
