Given that conducting a study, particularly a large-scale study (e.g., longitudinal study), requires a great deal of resources and effort, researchers want to prevent potential risks that may result in a study failing. One of the ways to prevent risks is to conduct a pilot study. A pilot study is a mini-study conducted with a small sample of participants prior to a primary study. This entry explains two primary goals of pilot studies, describes various approaches to pilot studies, and provides guidelines and suggestions for designing and conducting a pilot study.