The last century was marked by dazzling changes in many areas, such as technology and communications. Predictions into the second century of testing are seemingly difficult in such a context. Yet, looking back to the turn of the last century, Kirkpatrick (1900), in his American Psychological Association presidential address, presented fundamental desiderata for ability testing that in fact guides major testing research even today (normative age standards, emphasis on culture-general tasks, simultaneous measurement of many persons and adult ability measurement). An overview of the last century, presented in this address, shows that most fundamental principles in psychometrics and testing were available by 1930. With a few notable exceptions, the remainder of the last century of testing was devoted to applying or refining these principles. It is predicted that the same pattern will occur in this century of testing. Further developments in model-based measurement and in applying cognitive psychology principles in testing, intermingled with technology, will guide ability testing throughout the next century. These changes, to be elaborated in detail, include fundamental changes in test development procedures, the nature of the measuring tasks, aspects of ability that are measured, and types of interpretations given to ability. (Contains 8 figures and 3 tables.)