[en] GENIEsim, the GENIE simulation software, is an IDL-based code to simulate future observations with the Ground-based European Nulling Interferometer Experiment, which should be commissioned on the Very Large Telescope Interferometer (VLTI) in 2007. The code simulates operation in the mid-infrared (L' and N bands) and includes all major noise sources. The atmospheric turbulence is described by a Kolmogorov power spectrum, from which random time series are computed for perturbations to the optical paths. The effect of turbulence is reduced by means of control loops, which are either included in the VLTI facility (MACAO, PRIMA) or specific to the GENIE instrument. The output of GENIEsim is a time series of fluxes computed by integration of a source field multiplied by the GENIE transmission map, projected onto the plane of the sky. Simulations have already allowed to identify critical points in the design of the instrument, such as OPD and dispersion control, calibration of stellar leakage and background subtraction.