I will talk about astrophysical compact objects g on various properties of neutron stars. A neutron star (NS) is a remnant of stellar collapse (supernova) and is supported against gravity by neutron degeneracy pressure predicted by Pauli's exclusion principle. Since the first discovery in 1967, many more NSs are discovered, and our understanding of theoretical/observational properties of NSs have improved significantly, yet there are still a lot of issues to address. In this talk, I will review fundamental physics in NSs and recent progress in observational and theoretical works.