 The Ergodic Hierarchy (EH) is a central part of ergodic theory. It is a hierarchy of properties that dynamical systems can possess. Its five levels are ergodicity, weak mixing, strong mixing, Kolmogorov, and Bernoulli. Although EH is a mathematical theory, its concepts have been widely used in the foundations of statistical physics, accounts of randomness, and discussions about the nature of chaos, as well as in other sciences such economics. We introduce EH and discuss its applications.