Magnetic fields are a fundamental component of the physical world on all scales—as constituents of the electromagnetic environment of all matter. The interaction between the magnetic fields and matter is at the heart of many dynamic processes that shape astrophysical objects and their environments. Regions of space threaded by magnetic fields control or at least influence the interactions that take place between them. Observing and understanding magnetic fields and the role they play in physical processes in the solar system and beyond have been the subject of a series of Workshops and publications by the International Space Science Institute since 2008. The first three volumes covered the origin and dynamics of solar magnetism, the magnetic fields of the planets, and the magnetic field of the Earth. These were meant to constitute a trilogy of magnetic fields within the confines of the solar system. Then came the fourth volume which extended the coverage to the whole Universe, but concentrating on large-scale magnetic fields, comparable to, or smaller in magnitude than those directly measured within the solar system. The four volumes are: