This article presents the results of an investigation of whether the personality characteristics and behavioral tendencies of effective organization development (OD) consultants differ significantly from those of less effective ones. From an extensive review of the literature by the author and a panel of three judges, three categories of characteristics were derived for testing: openness and responsiveness to others' needs and concerns, comfort with ambiguity and the ability to make sense of it, and comfort with oneself in relation to others. The study subjects, 105 OD consultants in the U.S. Navy, completed three personality instruments. Peers, fellow consulting team members, and superiors of these consultants (also OD consultants) also rated the subjects' consulting effectiveness. Multivariate analyses showed a strong, significant relationship between consultant effectiveness and the characteristics assigned to the three categories. The results strongly support the hypotheses that the personality characteristics and individual tendencies of effective OD consultants differ significantly from those of less effective consultants.