Sensitivity, to be able to detect a difference or change when there is one, is essential to measurement practice. Yet, little research has been done that covers this topic, and it is basically ignored in instrument construction. As a result, many so-called valid and reliable instruments are useless. This tutorial is to provide an overview on sensitivity—what it is, why it is important, and how to determine/evaluate it. Common statistical methods/software will be introduced and application examples illustrated.