To gain insight into nucleation mechanisms and evaluate rates, an appropriate simulation methodology must be chosen to investigate the system at hand. This flow diagram identifies where theory-based simulation methods (based on CNT and its extensions) are most suitable. In particular, we highlight that secondary nucleation typically involves interactions of crystalline particles with the fluid at a scale inaccessible to molecular simulations and, with some notable exceptions , it is typically outside the scope of atomistic simulation studies. Heterogeneous nucleation is only partly included in the applicability domain as, while most methods discussed in this review are in principle, applicable examples exist only for crystal nucleation from the melt .