Stimuli that have been used to operate responsive molecular systems and materials include heat, pH, ions, electric fields, magnetic fields, mechanical forces, sound, light, microwaves, molecular recognition, changes in solvent polarity, and chemical reactions, in addition to redox events. Compared with the other stimuli, redox is attractive in that it can simultaneously alter the charge and spin states of a molecule and its ensembles. Redox stimuli can be generated either by voltage application or action of oxidants/reductants. Photoirradiation sometimes can cause oxidation or reduction by electron transfer. Depending on the redox states, the number of associated counterions changes. This variation can affect the solvation properties of redox-active molecules and stabilities of their ensembles. As a consequence, substantial changes in related physical properties such as optical, magnetic, and mechanical properties can be expected. Also noteworthy is that redox-responsive systems have the potential advantage for industrial applications, because they can, in principle, be readily incorporated into existing technologies for electronic devices.The redox-active molecular motifs that have been the subject of extensive studies are listed in Figure 1. In redox events, these molecules behave in a predictable manner, because their oxidized and/or reduced states are reasonably stable. In particular, ferrocene (Fc) has been used frequently because its oxidized state (Fc + ) is remarkably stable. Aromatic compounds such as alkyl viologen (RV 2+ ), tetrathiafulvalene (TTF), oligothiophenes, and naphthalene diimide (NDI) and their analogs have been widely utilized for the construction of redox-responsive molecular systems and materials. In general, these planar π-conjugated molecules are thought to assemble homotropically and/or hybridize heterotropically with other π-conjugated modules to form π-stacked columnar architectures. Needless to say, the structural stability of such architectures depends on the electronic states of these redox-active constituents. Disulfide is a different type of redox-active motif that can be cleaved off reductively and regenerated oxidatively. This reversible feature provides a dynamic covalent chemistry [31] in relation to biological systems where glutathione (GSH) produced in an intracellular environment serves as a typical reductant for S-S bonds. Using this redox chemistry, hollow capsules that break up into small fragments after cellular uptake have been developed. Tris(bipyridine)ruthenium (Ru(bpy) 3 ) is a representative catalyst for the Belousov-Zhabotinsky (BZ) reaction, which enables autonomous oscillatory chemical transformations. Figure 1 shows how redox-active motifs are integrated into systems for utilization. Depending on the number of Redox reactions can alter the electronic, optical, and magnetic properties of molecules and their ensembles by adding or removing electrons. Here, the developments made over the past 10 years using molecular events are discussed, such as assembly/disa...