Generalized anxiety disorder (GAD) is one of the most common anxiety disorders and related to individuals’ various forms of psychological dysfunction. To assess individuals’ anxiety symptoms, a brief, clinical, and self-report 7-item Generalized Anxiety Disorder Scale (GAD-7) was developed. The original GAD-7 scale was verified as a valid and efficient tool for screening for GAD and assessing its severity in clinical practice and research. Researchers have also extended the GAD-7 to other populations (i.e., the general population) and translated it into different languages. The purpose of the current chapter was to summarize the psychometric properties of the GAD-7 scale in the initial version as well as various adapted versions in other languages. We also reviewed the subsequent evidence on the validation of the GAD-7 scale among diverse populations. Furthermore, we illustrated the ways to use this measure, discussed its limitations, and proposed future research directions.