As part of the work at FOI on 3D laser radar, we have developed FOI-LadarSim, a computer model to simulate sensor data from 3D laser radar sensors. This report describes the physical theories used to simulate 3D laser radar sensors, as well as it shows examples on systems and applications it has been adapted to. The report also holds a brief description of the implementation and thoughts on future development. The model is divided into four main components; the laser source, the atmosphere, the scene and the receiver. These four steps are sequentially processed using a method similar to ray tracing, where the laser source is treated as a large amount of weaker laser sources distributed over the laser beam. These are treated individually and by using fairly simple calculations, a spatially high accuracy can be achieved throughout the simulations. The model is adaptable to a big number of tasks such as;  illustrate the ability with 3D laser radar when real data is missing  generate training data for algorithm development for detection and recognition algorithms  connect the 3D laser radar sensor to more abstracted simulations  test and evaluate new sensors settings by extending system parameters  test and evaluate sensors in different settings/environments. FOI has primarily used the model for the first three purposes. The model development has been going on for several years and the implementation has now reach modularity, which will simplify further development and maintenance, or adaptations to new tasks.