This chapter introduces theory that undergirds the role of testing adaptations in assessment, provides examples of item modifications and testing accommodations, reviews research relevant to each, and introduces a new paradigm that incorporates opportunity to learn (OTL), academic enablers, testing adaptations, and inferences that can be made from scores. The purpose is to document the substantial research that has been completed on testing adaptations, along with critical findings, and to push the field to reexamine the methods that are used to answer questions about the appropriateness of the evidence that has typically been collected.