An action-oriented taxonomy of errors in human-computer interaction in the office differentiated four classes: functionality problems, usability problems, interaction problems, and inefficient behavior. Functionality problems were differentiated in how they affect the action process. Usability problems were differentiated according to levels of action regulation and steps in the action process. For example, conscious strategies were differentiated from automatic ones. To examine the taxonomy's construct validation, several hypotheses regarding error-handling time, need for external support, complexity at work, and novices versus experts were tested in a field study of 198. © 1992, Taylor & Francis Group, LLC. All rights reserved.