THEMIS represents the most ambitious coordinated multi-spacecraft and ground-based programme ever attempted. It is expected that this mission will dramatically increase our understanding of the substorm process. In the years leading up to the launch of the five THEMIS probes, the four-spacecraft Cluster mission has defined the state of the art in the field of multi-spacecraft/ground-based investigations of the geospace environment. Hitherto unprecedented coordination of space- and ground-based experiments have yielded multi-point (in situ and remotely sensed) measurements of magnetospheric structure and dynamics. The overlap of the Cluster and THEMIS missions presents an excellent opportunity to move the multi-point measurement technique to the next stage. Since the apogees of the Cluster and THEMIS satellites orbits are separated by nearly 12 hour of local time, the synergy of these two missions and ground- based experiments will allow the detailed observation of solar wind-magnetosphere-ionosphere on both the day and nightside of the Earth. Several experimental scenarios will be presented.