The Magma Chamber Simulator is an open system thermodynamic model for computing the evolution of a magma body as it thermally and reactively interacts with surrounding country rock via partial melting and/or stoping and undergoes independent magma recharge (replenishment) during cooling and crystallization. The composite system consists of three sub-systems: resident Magma, Wallrock, and multiple (0 to 5) Recharge magma reservoirs. The MCS uses one of four MELTS phase equilibria engines intimately coupled to a user-defined exec (IGOR) to track and report phase equilibria and major element, trace element and isotopic conecentrations within all multiphase-multicomponent sub-systems self-consistently based on rigorous equilibrium thermodynamics. The flexible user-interface affords many options that can be ideally tailored to model specific natural systems or model analogs. For example, in addition to full RnAFC (n = 0 to 5) simulations, it is easy to run AFC, RFC or simply FC simulations by minor changes of the input MES_name file used to define the initial conditions for a particular petrological scenario. The MCS is under continuous development with timely releases as new functionality is installed. The MCS supersedes an earlier generation of EC-RAFC geochemical-petrological models. MCS supports up to 48 trace elements including the radiogenic elements (Sr, Nd, 206Pb, 207Pb, 208Pb, Hf and Os) and the stable isotope oxygen, all of which may be of interest to geochemists and petrologists.