Various types of epoxide-amine networks based on diglycidyl ether of Bisphenol A (DGEBA), diglycidylaniline (DGA), or TGDDM were prepared, and the effect of the reaction mechanism on network formation, its structure, and properties was investigated. Structure evolution was followed, and fraction of the sol, equilibrium rubbery modulus, and glass transition temperature of nonstoichiometric networks were determined as a function of composition. Short-range cyclization was proved to be the main factor governing formation and structure of DGA-based networks, resulting in a nonnegligible sol fraction of the stoichiometric system. In contrast, the substitution effect in amine determines the structure evolution in the DGEBA-diamine networks. A theoretical model for formation of DGA-amine networks was developed, taking into account the full complexity of the reaction mechanism: cyclization, interdependent reactivity of epoxy and amine groups, homopolymerization by etherification, and ionic polymerization as well as formation of reactive intermediates. A reasonable agreement with experimental data in both amine and epoxide excess was obtained.