The goal of this project is to measure the properties of bulk matter at nuclear density. Neutron stars harbour the densest bulk matter and most intense electromagnetic fields in the Universe. Observing gravitational and electromagnetic radiation from neutron stars is the only way to study these extreme physical conditions. Studies of this kind probe a rich variety of fundamental physics, including the residual strong force between nucleons, which governs the equation of state of bulk nuclear matter, and phenomena such as nuclear superfluidity and superconductivity. Related astrophysics of fundamental interest includes the masses, spins, and moments of inertia of relativistic stars, and the structure and evolution of their magnetic fields.