The interaction of phonons with paramagnetic spin systems is best characterized by coupling constants which relate the energy shift in the spin system to the strain introduced into the lattice. The theory of spin-phonon interactions is reviewed, and the coupling constants, as experimentally obtained, are compared to those which are most conveniently calculated. Generally, the results calculated on the basis of the point-charge theory are in reasonable agreement with the experimental results. A number of special topics involving spinophonon interactions are discussed, including double quantum detection of phonons, propagation in a dispersive medium, and the phonon maser.