The structure of neutron stars is analyzed from both theoretical and observational perspectives. The radius of a neutron star is primarily determined by the pressure of matter near nuclear matter equilibrium density. If the pressure is not extremely soft, the radius is largely independent of mass and depends mainly on the pressure magnitude. For equations of state with extreme softening, the radius is more sensitive to mass. Accurate radius measurements can constrain the equation of state (EOS). The pressure near nuclear matter density is mainly a function of the nuclear symmetry energy, while the nuclear incompressibility and skewness parameters play secondary roles. The moment of inertia and binding energy of neutron stars are nearly universal functions of the star's compactness. These features are explained by considering analytic solutions to Einstein's equations, such as those by Buchdahl and Tolman. The fraction of the moment of inertia in the crust is a function of the star's compactness and the pressure at the core-crust interface. Observational studies of neutron star masses and radii show a narrow range of masses (1.25–1.44 M☉). Some X-ray binaries have higher masses, but these are not as well confirmed. A practical lower mass limit for neutron stars is about 1.1–1.2 M☉, based on the minimum mass of a proton-neutron star. Accurate mass measurements are available, but precise radius measurements are lacking. Observations of thermal emissions from neutron stars yield estimates of the radiation radius, R∞, which is related to the actual radius. However, these estimates are often small, suggesting that radiation may originate from polar hot spots rather than the surface. Quasi-Periodic Oscillations (QPOs) from X-ray emitting neutron stars provide a way to limit their masses and radii. The frequencies of QPOs are related to the neutron star's spin frequency and orbital frequencies. The beat frequency model suggests that the highest frequency, ν₂, is associated with the Keplerian frequency of inhomogeneities in an accretion disc. The lowest frequency, ν₁, is associated with a beat frequency between ν₂ and the star's spin frequency. These frequencies are related to the neutron star's spin frequency, ν, by ν₂ = √(ν₁² + (ν/2π)²). The discovery of isolated, non-pulsing neutron stars, such as RX J185635-3754, provides new opportunities to determine their radii. The X-ray flux of this star, combined with a best-fit blackbody temperature, yields an estimate of R∞. However, discrepancies between X-ray and optical fluxes suggest the need for more precise atmospheric modeling. The predicted spectrum of a heavy element atmosphere is consistent with observations, while a light element atmosphere is not. The paper discusses various equations of state (EOSs) used to model neutron star structure, including nonrelativistic potential models, relativThe structure of neutron stars is analyzed from both theoretical and observational perspectives. The radius of a neutron star is primarily determined by the pressure of matter near nuclear matter equilibrium density. If the pressure is not extremely soft, the radius is largely independent of mass and depends mainly on the pressure magnitude. For equations of state with extreme softening, the radius is more sensitive to mass. Accurate radius measurements can constrain the equation of state (EOS). The pressure near nuclear matter density is mainly a function of the nuclear symmetry energy, while the nuclear incompressibility and skewness parameters play secondary roles. The moment of inertia and binding energy of neutron stars are nearly universal functions of the star's compactness. These features are explained by considering analytic solutions to Einstein's equations, such as those by Buchdahl and Tolman. The fraction of the moment of inertia in the crust is a function of the star's compactness and the pressure at the core-crust interface. Observational studies of neutron star masses and radii show a narrow range of masses (1.25–1.44 M☉). Some X-ray binaries have higher masses, but these are not as well confirmed. A practical lower mass limit for neutron stars is about 1.1–1.2 M☉, based on the minimum mass of a proton-neutron star. Accurate mass measurements are available, but precise radius measurements are lacking. Observations of thermal emissions from neutron stars yield estimates of the radiation radius, R∞, which is related to the actual radius. However, these estimates are often small, suggesting that radiation may originate from polar hot spots rather than the surface. Quasi-Periodic Oscillations (QPOs) from X-ray emitting neutron stars provide a way to limit their masses and radii. The frequencies of QPOs are related to the neutron star's spin frequency and orbital frequencies. The beat frequency model suggests that the highest frequency, ν₂, is associated with the Keplerian frequency of inhomogeneities in an accretion disc. The lowest frequency, ν₁, is associated with a beat frequency between ν₂ and the star's spin frequency. These frequencies are related to the neutron star's spin frequency, ν, by ν₂ = √(ν₁² + (ν/2π)²). The discovery of isolated, non-pulsing neutron stars, such as RX J185635-3754, provides new opportunities to determine their radii. The X-ray flux of this star, combined with a best-fit blackbody temperature, yields an estimate of R∞. However, discrepancies between X-ray and optical fluxes suggest the need for more precise atmospheric modeling. The predicted spectrum of a heavy element atmosphere is consistent with observations, while a light element atmosphere is not. The paper discusses various equations of state (EOSs) used to model neutron star structure, including nonrelativistic potential models, relativ