Ionospheric tomography has matured into a reliable technique for sensing the propagation environment. The method enables images to be created of ionospheric electron density over a wide spatial region from observations made at a limited number of ground stations, thus complementing and extending some well established sounding methods for the monitoring of space plasma, Tomographic imaging has a role to play in the routine sensing of the ionised atmosphere, for use in applications involving ionospheric and trans-ionospheric propagation. In addition, the method can be applied to investigations of the ionospheric plasma, with particular application in regions where an inhospitable terrestrial environment makes conventional ground-based observations difficult or even impossible. (3 pages)