Human performance technology (HPT) has over 30 years of practice in real working settings and research in academia. The application of HPT principles, strategies, and models is aimed at solving performance problems and improving performance at all levels. Performance is the key word, and to improve performance is the value that HPT brings to individuals, organizations, and society. This article addresses questions centering on performance: 1) Where does the word performance come from? 2) What does performance really mean in HPT? And 3) what is HPT studying about performance? The concept of performance comes from Gilbert’s notion of worthy performance which distinguishes behavior from accomplishment. Specifically, accomplishment is the positive and valued outcomes of behavior and the transaction from behavior to accomplishment is the performance that HPT focuses on. Performance is not a simple term, but a complex system in which factors are interacting with each other to affect performance. As a science of performance, HPT applies systematic approaches to investigate the relationship between and interaction among the affecting factors in a performance system.