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A simple cosmological model with only six parameters (matter density, Ω m h 2, baryon density, Ω b h 2, Hubble constant, H 0, amplitude of fluctuations, σ 8, optical depth, τ, and a slope for the scalar perturbation spectrum, n s) fits not only the 3 year WMAP temperature and polarization data, but also small-scale CMB data, light element abundances, large-scale structure observations, and the supernova luminosity/distance relationship. Using WMAP data only, the best-fit values for cosmological parameters for the power-law flat Λ cold dark matter (ΛCDM) model are (Ω m h 2, Ω b h 2, h, n s, τ, σ 8)=(0.1277, 0.02229±0.00073, 0.732, 0.958±0.016, 0.089±0.030, 0.761). The 3 year data dramatically shrink the allowed volume in this six-dimensional parameter space. Assuming that the primordial fluctuations are adiabatic with a power-law spectrum, the WMAP data alone require dark matter and favor a spectral index that …