This paper summarizes the properties of strongly correlating liquids, i.e.,
liquids with strong correlations between virial and potential energy
equilibrium fluctuations at constant volume. We proceed to focus on the
experimental predictions for strongly correlating glass-forming liquids. These
predictions include i) density scaling, ii) isochronal superposition, iii) that
there is a single function from which all frequency-dependent viscoelastic
response functions may be calculated, iv) that strongly correlating liquids are
approximately single-parameter liquids with close to unity Prigogine-Defay
ratio, and v) that the fictive temperature initially decreases for an isobaric
temperature up jump. The "isomorph filter", which allows one to test for
universality of theories for the non-Arrhenius temperature dependence of the
relaxation time, is also briefly discussed
