PhoSim is an optical ray tracing Monte-Carlo simulator capable of reproducing the physical processes taking place in a tissue environment when illuminated by Near-Infrared radiation. From a macroscopic point of view this can be accomplished by the proper manipulation of the Henyey-Greenstein phase parameter g, which represents a simple and analytical solution for the fast generation of a random scattering angle photon distribution. Microscopically, the program can simulate certain biological structures by placing a proper density of sub-cellular organelles inside the volume of interest, proportional to the wavelength of the radiation used at the study (∼750-1000 nm). The new version of this software package is able to create different type of phantoms in multi-layer environments and it is also equipped with a detailed Fate and Time of Flight information of each traveling photon. PHOSIM is a simple and useful tool for Time-Resolved Optical Tomographic studies; its basic functions and capabilities with optical tomographic examples are presented in this work.