  (Abridged) The WMAP 5-year data strongly limit deviations from the minimal
LCDM model. We constrain the physics of inflation via Gaussianity,
adiabaticity, the power spectrum shape, gravitational waves, and spatial
curvature. We also constrain the properties of dark energy, parity-violation,
and neutrinos. We detect no convincing deviations from the minimal model. The
parameters of the LCDM model, derived from WMAP combined with the distance
measurements from the Type Ia supernovae (SN) and the Baryon Acoustic
Oscillations (BAO), are: Omega_b=0.0456+-0.0015, Omega_c=0.228+-0.013,
Omega_Lambda=0.726+-0.015, H_0=70.5+-1.3 km/s/Mpc, n_s=0.960+-0.013,
tau=0.084+-0.016, and sigma_8=0.812+-0.026. With WMAP+BAO+SN, we find the
tensor-to-scalar ratio r<0.22 (95% CL), and n_s>1 is disfavored regardless of
r. We obtain tight, simultaneous limits on the (constant) equation of state of
dark energy and curvature. We provide a set of "WMAP distance priors," to test
a variety of dark energy models. We test a time-dependent w with a present
value constrained as -0.33<1+w_0<0.21 (95% CL). Temperature and matter
fluctuations obey the adiabatic relation to within 8.9% and 2.1% for the axion
and curvaton-type dark matter, respectively. The TE and EB spectra constrain
cosmic parity-violation. We find the limit on the total mass of neutrinos,
sum(m_nu)<0.67 eV (95% CL), which is free from the uncertainty in the
normalization of the large-scale structure data. The effective number of
neutrino species is constrained as N_{eff} = 4.4+-1.5 (68%), consistent with
the standard value of 3.04. Finally, limits on primordial non-Gaussianity are
-9<f_{NL}^{local}<111 and -151<f_{NL}^{equil}<253 (95% CL) for the local and
equilateral models, respectively.
