The effects of crosslink functionality (f(c)), molecular weight between crosslinks (M-c), and chain stiffness display on the thermal and mechanical behavior of epoxy networks are determined. Both f(c) and M-c are controlled by blending different functionality amines with a difunctional epoxy resin. Chain stiffness is controlled by changing the chemical structure of the various amines. In agreement with rubber elasticity theory, the rubbery moduli are dependent on f(c) and M-c, but independent of chain stiffness. The glassy moduli and secondary relaxations of these networks are relatively independent of f(c), M-c, and chain stiffness. However, the glass transition temperatures (T-g) of these networks are dependent on all three structural variables. This trend is consistent with free volume theory and entropic theories of T-g. f(c), M-c, and chain stiffness control the yield strength of these networks in a manner similar to that of T-g, and is the result that both properties involve flow or relaxation processes. Fracture toughness, as measured by the critical stress intensity factor (K-Ic), revealed that f(c) and M-c are both critical parameters. The fracture behavior is the result of the fracture toughness being controlled by the ability of the network to yield in front of the crack tip.