Both clinical and personality psychologists are interested in assessing personality change, although they have tended to approach the issue in different ways. In this paper we argue that both sub-fields should focus more on basic issues in the assessment of personality change, and that they would make more progress on this issue together than alone. This Special Section on the Assessment of Personality Change includes four papers by researchers working primarily in basic personality science. Each paper addresses specific ways to advance the assessment of personality change that have both basic and applied clinical relevance, but collectively they show how far the field still has to go.