The aim of this paper is to investigate and quantify the effect of the rigidity and mobility of the reactive groups and of the functional group spatial density and to give an insight into the role these factors play in the polymerization of epoxy :resins. The effect of the epoxy molecular architecture on the reactivity with amine curing agents has been studied using different, epoxy-containing compounds with various configurations. DGEBA cured with isophorone diamine has been used as a reference system. Dendritic hyperbranched polymers (HBP) with epoxy groups grafted on the shell and two aliphatic epoxidized model compounds have been used to investigate the effects of chemical composition, solubility, mobility, and spatial density of reactive groups. Mobility of the reactive groups, which is inversely related to the molar stiffness, has been found to affect the mechanism of reaction, changing an autocatalytic reaction for DGEBA-amine systems into a noncatalytic reaction for HBP-amine systems. The reactive group molecular density was found to be responsible for an increase in the activation energy.