Assessment instruments are critical to assist in the selection and development of strong, effective leaders. Developing a strong understanding of what makes a tool empirically sound, based on solid scientific concepts, can mean the difference between choosing an assessment that provides targeted, actionable, and accurate information versus an instrument that yields information that is biased, unhelpful, or even harmful to individuals and organizations. This article discusses the history of leadership assessments and how to critically evaluate available leadership instruments in order to enhance decision-making about what tool to use.