Technology development in human-computer interaction (HCI) can be interpreted as a coevolution of tasks and artifacts. The tasks people actually engage in (successfully or problematically) and those they wish to engage in (or perhaps merely to imagine) define requirements for future technology and, specifically, for new HCI artifacts. These artifacts, in turn, open up new possibilities for human tasks, new ways to do familiar things, and entirely new kinds of things to do. In this article, we describe psychological design rationale as an approach to augmenting HCI technology development and to clarifying the sense in which HCI artifacts embody psychological theory. A psychological design rationale is an enumeration of the psychological claims embodied by an artifact for the situations in which it is used. As an example, we present our design work with the View Matcher, a Smalltalk programming environment for coordinating multiple views of an example application. In particular, we show how psychological design rationale was used to develop a view matcher for code reuse from prior design rationales for related programming tasks and environments.