The Wilkinson Microwave Anisotropy Probe (WMAP) 5-year data provide stringent constraints on deviations from the minimal, 6-parameter ΛCDM model. These constraints are used to study cosmic inflation, dark energy, neutrinos, and non-Gaussianity. The 68% uncertainties on the cosmological parameters derived from the WMAP data, combined with Type Ia supernova (SN) and Baryon Acoustic Oscillation (BAO) measurements, are: Ω$_h h^2 = 0.02267^{+0.00058}$, Ω$_m h^2 = 0.1131 \pm 0.0034$, Ω$_\Lambda = 0.726 \pm 0.015$, $n_s = 0.960 \pm 0.013$, τ = 0.084 ± 0.016, and Δ$^R_k = (2.445 \pm 0.096) \times 10^{-9}$ at $k = 0.002$ Mpc$^{-1}$. The analysis constrains the spatial curvature, Gaussianity, adiabaticity, and power spectrum of primordial fluctuations. It also tests models of dark energy, including the equation of state, parity-violating interactions, and neutrino properties. No significant deviations from the minimal model are detected. The results provide tight limits on the tensor-to-scalar ratio, the amplitude of primordial gravitational waves, and the spatial curvature of the universe. The nature of dark energy is explored through its equation of state and parity-violating interactions. Neutrino properties, such as mass and the number of species, are constrained. The analysis also examines the non-Gaussianity of primordial fluctuations, finding limits on the local and equilateral non-Gaussianity parameters.The Wilkinson Microwave Anisotropy Probe (WMAP) 5-year data provide stringent constraints on deviations from the minimal, 6-parameter ΛCDM model. These constraints are used to study cosmic inflation, dark energy, neutrinos, and non-Gaussianity. The 68% uncertainties on the cosmological parameters derived from the WMAP data, combined with Type Ia supernova (SN) and Baryon Acoustic Oscillation (BAO) measurements, are: Ω$_h h^2 = 0.02267^{+0.00058}$, Ω$_m h^2 = 0.1131 \pm 0.0034$, Ω$_\Lambda = 0.726 \pm 0.015$, $n_s = 0.960 \pm 0.013$, τ = 0.084 ± 0.016, and Δ$^R_k = (2.445 \pm 0.096) \times 10^{-9}$ at $k = 0.002$ Mpc$^{-1}$. The analysis constrains the spatial curvature, Gaussianity, adiabaticity, and power spectrum of primordial fluctuations. It also tests models of dark energy, including the equation of state, parity-violating interactions, and neutrino properties. No significant deviations from the minimal model are detected. The results provide tight limits on the tensor-to-scalar ratio, the amplitude of primordial gravitational waves, and the spatial curvature of the universe. The nature of dark energy is explored through its equation of state and parity-violating interactions. Neutrino properties, such as mass and the number of species, are constrained. The analysis also examines the non-Gaussianity of primordial fluctuations, finding limits on the local and equilateral non-Gaussianity parameters.