This document provides a decision tree to help determine if an activity constitutes human subjects research under 45 CFR 46. It involves asking a series of yes or no questions to evaluate if the activity is a systematic investigation designed to develop generalizable knowledge, involves obtaining private information about living individuals, and involves intervention or interaction with those individuals. If the answers indicate it is research involving human subjects, it may require IRB review unless an exemption applies under 45 CFR 46.101(b)(1)-(6).