A countercurrent flow reactor (CFR) is an autothermal reactor, in which the reactants flow countercurrently at equal velocities and flow rates through two compartments, with negligible heat-transfer resistance between the two sections. Two-reactor configurations can be used: a "regular" one, in which the two components are fed by two separate feeds; a "folded" configuration, in which a single feed flows first through one compartment and then reverses its direction and flows countercurrently in the second. Temperature and concentration profiles in the regular CFR configuration usually have mirror symmetry around its center Under cooling, however, asymmetric steady-state profiles may form. The interaction between the heat removed by the effluents and by cooling through the wall may generate complex periodic or even chaotic states. The temperature and concentration profiles in a folded CFR are the same as those attained in a regular CFR, which are symmetric around the reactor center: The imposed symmetry causes the steady-state and dynamic features of the folded CFR to be less complicated than those of the regular CFR and is less likely to cause operational problems. Boundaries of parameter regions with qualitatively different features for both CFR configurations were constructed by the method of Khinast et nl. (1998a). The analysis of the CFR enhances the understanding of similar dynamics observed in a reverse-flow reactor.