AbstractIn this chapter we first set the stage by focusing on the concept of validity, documenting key changes over time in how the term is used and examining the specific ways in which the concept is instantiated in the domain of personnel selection. We then move from conceptual to operational and discuss issues in the use of various strategies to establish what we term the predictive inference, namely, that scores on the predictor measure of interest can be used to draw inferences about an individual's future job behavior or other criterion of interest. Finally, we address a number of specialized issues aimed at illustrating some of the complexities and nuances of validation.