Consistent with the conceptualizations of participation and involvement in psychology, organizational behavior, consumer behavior, and other disciplines, this paper redefines the participation construct to distinguish its behavioral and psychological dimensions. 'User participation" is defined as the observable behavior of information system users in the information system development process; "user involvement" as a need-based attitude or psychological state of users with regard to that process and to the resultant information system; and "user engagement" as the set of user behaviors and attitudes toward information systems and their development. A field study was conducted in a $40 billion interstate bank during the installation and conversion of an information system. A questionnaire was developed, pre-tested, and validated for internal consistency, temporal stability, factorial validity, and multicollinearity. Path analysis was used for theorytesting (i.e., model comparison). There was strong empirical evidence to support: (1) that user involvement is something distinct from, although associated with, user participation; (2) that this psychological state of user involvement may be more important than user participation in understanding information system success; (3) that the behavioral-attitudinal theory of information system success (i.e., that participation "causes" involvement which mediates the participation-success relationship) is superior to the behavioral theory (i.e., participation "causes" success); and (4) that user engagement during the installation phase is strongly associated with user satisfaction.