As the curing protocol proceeds, the liquid turns into a gel. The point of gelation for a crosslinking system is defined as the extent of reaction corresponding to incipient chemical network formation. According to the classical Flory-Stockmayer 60,61 theory of polymerization, gelation coincides with the emergence of a macroscopic molecule, the "gel", which extends throughout the volume of the mixture and whose mass is far greater than that of single monomers. Traditionally, gelation has been measured from MD data only indirectly, by looking for significant changes in some physical or structural properties related to the inception of network formation. This usually includes the largest mass buildup, the onset of intramolecular polymerization reactions or the reduced molecular weight (RMW). Recently, we have investigated the limitations of these methods and introduced a rigorous algorithmic procedure to exactly measure the gel point in MD simulations. Our strategy measures the gel point as a percolation transition. In the limit of a macroscopic system, in which the size of the network is by far greater than the size of any single monomer, the periodic percolation threshold approaches the actual percolation point of the system. A portrait of one of our cross-linking epoxy models at the point of periodic percolation is given in Figure .