In this paper we address the development of mechanical stress in catalytic and noncatalytic reacting systems. The thermoelastic formulation is presented and discussed as it applies to several examples of practical importance. These include fracture of catalyst pellets due to thermal stress, application of stresses during rapid cooling of reacted samples, and stress development during noncatalytic reactions in powders or particles. Stresses develop as a result of temperature gradients due to heat effects of the reaction, and differences in expansion coefficients and equivalent volume of different phases. The examples cited in this review illustrate that stresses play an important role in the design of chemical reactors and may change the reaction characteristics, in both a qualitative and quantitative way.