This chapter describes Irradiation Driven Molecular Dynamics (IDMD) — a novel computationalmethodology for atomistic simulations of the irradiation-driven transformations of complex molecular systems, implemented in the MBN Explorer software package. Within the IDMD framework various quantum processes occurring in an irradiated system are treated as random, fast and local transformations incorporated into the classical MD framework in a stochastic manner with the probabilities elaborated on the basis of quantum mechanics. Major transformations of irradiated molecular systems (such as topological changes, redistribution of atomic partial charges, alteration of interatomic interactions) and possible paths of their further reactive transformations can be simulated by means of MD with reactive force fields, in particular with the reactive CHARMM (rCHARMM) force field implemented in MBN Explorer. This chapter reviews the general concept of the IDMD methodology and the rCHARMM force field and provides several exemplary case studies illustrating utilization of these methods.