It is known that neutron stars, like other stars without convection, contain a "fossil" magnetic field. I examine how the magnetic field left over from the initial neutrino-driven convective phase relaxes into a long-lived state, and also touch on the processes by which this field will evolve on a longer timescale. Before briefly looking at some observational effects such as gravitational wave emission from millisecond magnetars, and stars with similar rotation periods and dipole fields but with very different observational properties, I move to larger scales, examining the bubbles seen in X-ray images of galaxy clusters. Via consideration of the properties of magnetised AGN ejecta, I make some predictions regarding the magnetic state of these bubbles and the consequences thereof, such as particle acceleration and inhibition of shredding instabilities.
