If bulk or thin-film ceramics consisting of more than one component are subjected to a high temperature during processing or use, interfacial solid–solid reactions occur between the components. To understand this type of reactions, the atomic structure of various reactive oxide/pyrochlore and oxide/spinel model interfaces is studied by high-resolution transmission electron microscopy. Kinetics of the pyrochlore- and spinel-forming reactions at these interfaces are shown to depend on the atomic structure of the interface, in particular on that of the interfacial dislocations. During the reaction, these dislocations have to move together with the advancing interface. Accordingly, reaction kinetics are determined by the mode of dislocation movement and, thus, by the Burgers vector geometry of the interfacial dislocations. The type of interfacial dislocations is, in turn, influenced by the stress conditions during the initial stage of the solid state reaction.