Book excerpt: Neutron stars, the most extreme state of matter yet confirmed, are responsible for much of the high-energy radiation detected in the universe. Mèszàros provides a general overview of the physics of magnetized neutron stars, discusses in detail the radiation processes and transport properties relevant to the production and propagation of high-energy radiation in the outer layers of these objects, and reviews the observational properties and theoretical models of various types of neutron star sources.