  The magnetic domain configuration of a system reveals a wealth of information
about the fundamental magnetic properties of that system and can be a critical
factor in the operation of magnetic devices. Not only are the details of the
domain structure strongly governed by materials parameters, but in thin-films
and mesoscopic elements the geometry has an often pivotal effect, providing a
convenient handle to tailor desired domain states. Furthermore a full
understanding of a system requires, in addition, investigation of the dynamic
evolution of the spin-state, which is of particular importance for applications
relying on e.g. the switching of magnetic elements. Here we review some of the
main modern techniques for magnetic imaging, highlighting their respective
advantages and limitations. The methods for imaging domain configurations and
spin structures cover various spatial and temporal resolution scales and
encompass those based on electron and x-ray microscopy as well as scanning
probe techniques. Furthermore, away from the discipline of condensed-matter
physics, magnetic effects are instrumental in a number of techniques for
medical imaging, some key examples of which we also present.
