The Infrared Atmospheric Sounding Interferometer (IASI) is a Fourier-Transform Spectrometer (FTS) that will be launched on the European METOP meteorological platform. IASI is to be used operationally to derive vertical profiles of temperature, humidity and composition of the atmosphere. This paper describes the IASI simulator model (ISM) developed in order to generate realistic instrument data measurements needed to test the signal processing algorithms as well as test performance improvement and measurement software. The simulator takes as input an atmospheric or calibration scene and a detailed description of the instrument parameters and produces a realistic sampled interferogram out of the Analog to Digital Converter (ADC). The instrument model includes all FTS relevant optical, mechanical and electronic phenomena such as: self-emission, double modulation, spectrum channel, position and time-dependent shear, position and time-dependent tilt, speed fluctuations, finite field of view, chromatism, noise, detector non-linearity, sampling laser wavelength and power fluctuations, etc. Both the science and the metrology signals are simulated. The validated models come from the heritage of a simulator developed 8 years ago for the ESA Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) that have evolved with various internal projects. A software tool coded in JAVA-2 and running on Windows based system integrates all the models. A graphical user-interface allows the edition of input parameters, the generation of intermediary results (modulation efficient, Instrument Line Shape (ILS), spectral power on the detector, etc.) and the visualization of results.