The influence of temperature and the extent of curing on the viscosity of a reactive epoxy resin adhesive is described and a mathematical model for the behavior is introduced. The temperature dependence of viscosity can be described by the WLF equation. The parameters required for the WLF equation are obtained from experiments in the temperature range where the crosslinking reaction has not yet been initiated. The viscosity and glass transition temperature increase with increasing curing. The glass transition temperature can also be described with an equation of the WLF type. Kinetic experiments on the epoxy resin adhesive enable a time and temperature dependent description of the extent of curing with a series reaction of the type A-->B-->C, where each partial reaction is of order n. The viscosity model and reaction kinetics enable calculation of the viscosity as a function of time and temperature, which agrees well with the experimental data.