Mechanically interlocked molecules (MIMs) consist of molecular components held together through mechanical entanglement rather than covalent bonds, the two most common classes of which are catenanes (consisting of interlocked macrocycles) and rotaxanes (consisting of macrocyclic and dumbbell-shaped components). The entanglement and relative orientation of the components in MIMs creates a three-dimensional cavity space between them, enabling encapsulation of guest species (Fig. ). The mechanical bond has been exploited to tailor environments for the interlocked components themselves, essentially acting as kinetically stable host-guest assemblies. In this manner, mechanically-enforced proximity of components can alter the reactivity 204 of, or interactions 205 between, functional units. These effects of the mechanical bond have been investigated for applications in caging the activity of biomolecules, 206 catalysts 207 and cytotoxic agents, 208 just to name a few. The discussion in this review, however, will be limited to MIMs as hosts for guest ions/molecules that are distinct from the interlocked units.