Equation of state, neutron stars and exotic phases

The role of the equation of state in the structure of neutron stars is summarized. At densities beyond a few times the normal nuclear saturation density, the neutron-proton-electron sea can be supplemented with more exotic matter, usually involving strangeness, such as hyperons, kaon or pion condensates, and deconfined quark matter. In the case of a boson condensate or deconfined quark matter, the exotic matter may form a mixed-phase region with the hadronic matter. Global aspects of neutron stars, such as radii, moments of inertia and the maximum mass, can be related to specific properties of matter at selected density ranges. Recent observations of isolated neutron stars and pulsars in binaries are beginning to yield significant constraints on structural properties of neutron stars and hence on the properties and composition of neutron-rich nuclear matter.