Molecular dynamics computer simulations have been used to model desorption processes of energetic particle bombardment (SIMS, FABMS) as well laser ablation of organic films (MALDI). The results of the simulations are used to compare with experimental data and to provide microscopic insight into the fundamental events. The particle bombardment examples to be discussed include energy and angular distributions of ejected metal atoms and benzene molecules, mechanisms of ejection of organic molecules, and bombardment by cluster projectiles. Topics to be discussed from the laser ablation studies include microscopic mechanisms of ablation, an analytic expression of the velocity distribution of the plume and conditions for desorption of large molecules as in MALDI experiments. Further information can be found at http://galilei.chem.psu.edu/.