The engagement of external IS professionals to supplement in-house resources is a widespread and growing practice. Limited prior research on consultant engagement suggests client involvement is a key factor of success. With the objective of better understanding the antecedents of client involvement in computer system selection consultancies, several variations on Ajzen and Maddenís theory of planned behavior (TPB) are tested. Appreciating the potential power of the consultant to facilitate or block client involvement, a major variation on perceived behavioral control is the inclusion of the consultantís attitude toward involving the client. The resultant ìtwo-actorî model is tested using partial least squares and survey data from firms that engaged external consultants to assist with computer system selection. Client attitude alone has relatively low explana- tory power. The findings highlight the non-volitional nature of client involvement and the power of the consultant to block or facilitate that involvement.