If phenotypic plasticity is a trait subject to selection and evolution, we need to quantify reaction norms and to identify the potential target(s) of selection. Previously we proposed the use of polynomial coefficients as reaction norm descriptors. However, the interpretation of these coefficients is not straightforward if the reaction norm is not linear. Therefore, we instead propose the use of characteristic values to describe reaction norms. We depict such characteristic values for linear, quadratic, and logistic reaction norms, discuss how they might evolve, and illustrate their estimation using data on abdominal pigmentation of Drosophila simulans.