This definitional paper provides a chronological perspective of human performance technology (HPT) definitions and an evaluation of them in terms of independent and dependent variables. The intent is to compare the definitions with the goals that have been articulated for HPT over the years and to provide one source for past definitions as researchers move forward to continue their study of HPT. The search for definitions extended back to Gilbert in the late 1970s, who provided a foundation; the search revealed an evolution of definitions from the late 1970s to the present day, with the definition currently on the Website of the International Society for Performance Improvement (ISPI). The analysis depicts a brief chronology of the field, the breadth of HPT through the definitions, and how the definitions changed as the field matured (with the increased knowledge and applications of several theory disciplines).