  The name Ising has come to stand not only for a specific model, but for an
entire universality class - arguably the most important such class - in the
theory of critical phenomena. I review several examples, both in and out of
equilibrium, in which Ising universality appears or is pertinent. The
"Ornstein-Zernike" connection concerns a thermodynamically self-consistent
closure of the eponymous relation, which lies at the basis of the modern theory
of liquids, as applied to the Ising lattice gas. Debye and Huckel founded the
statistical mechanics of ionic solutions, which, despite the long-range nature
of the interaction, now appear to exhibit Ising-like criticality. The model of
Widom and Rowlinson involves only excluded-volume interactions between unlike
species, but again belongs to the Ising universality class.
Far-from-equilibrium models of voting behavior, catalysis, and hysteresis
provide further examples of this ubiquitous universality class.
