IRISIM is an imaging and video simulation program that models and simulates the entire imaging process of broadband and multispectral infrared imaging systems. IRISIM receives mono- and multi-spectral, high resolution flux images of infrared scenes, processes the imagery as a function of desired scenario and imagery, and generates the resultant imagery (still image or sequence), as it would appear on the operator's display or as an input to an image processing module. The physical models used in IRISIM are based on analytical and empirical models of the imaging process and are implemented in several main modules, including imager characteristics (e.g. optics, scanning, detector, dewar, electronics, display), imager-to-scene geometry, line of sight vibrations and environmental conditions. This paper provides an overview of IRISIM and presents preliminary results of a validation procedure which compares MRTD observer tests using IRISIM simulations to respective lab measurements of actual imagers and to MRTD predictions calculated by TRM3. The results of the validation process indicate a close fit between the compared data sets. Furthermore, IRISIM and TRM3 integration is currently considered as a future platform for IR system performance evaluation.