We investigate the interaction of multiple Coronal Mass Ejections (CMEs) in the inner heliosphere using three-dimensional global magnetohydrodynamic (MHD) models of the solar corona and the heliosphere. These studies are motivated by the need to better understand white-light observations of CME cannibalism by coronographs such as LASCO C3 and in-situ observations of multiple-magnetic clouds and complex ejecta by Wind/ACE. The simulations are also used to predict future observations by the Solar TErrestrial Relation Observatory (STEREO) Heliospheric Imagers and the Living With a Star (LWS) Sentinels.; Using models of the coronal magnetic field and solar wind representative of solar minimum conditions, we study the interaction of two successive CMEs propagating into the bi-modal solar wind. We also investigate the homologous eruptions from NOAA active region 9236 in November 24, 2000, using the Space Weather Modeling Framework (SWMF). For this simulation, the coronal magnetic field is reconstructed using magnetogram data, in order to reproduce solar maximum conditions. The ejections are initiated using out-of-equilibrium flux ropes. We produce synthetic white-light images of the halo CMEs and compare them to LASCO observations; we also compare the resulting complex fast streams at Earth with Wind measurements.; We find that the trailing shock remains at all times a fast-mode shock, until it merges with the leading shock. This merging leads to a large increase in the temperature across the shock and the formation of a contact discontinuity between the old and new downstream regions. The propagation of the trailing shock through the first magnetic cloud compresses, heats and accelerates the cloud. The presence of a compressed period of southward Bz will result in an increased geo-effectiveness. Additionally, the reconnection between the clouds results in the formation of a fast magnetosonic reverse shock, which compresses and slows down the trailing cloud.; This work represents the first self-consistent investigation of interacting CMEs and includes the first Sun-to-Earth simulation of real complex events. It also includes the first systematic investigation, based on three-dimensional simulations of a CME, of the accuracy of coronographic observations and of the methods used to derive CME mass and energetics.
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