This study investigated a personal disposition toward proactive behavior, defined as the relatively stable tendency to effect environmental change. We developed an initial scale to assess the construct and administered it to a sample of 282 undergraduates. Factor analysis led to a revised, unidimensional scale with sound psychometric properties. A second sample of 130 undergraduate students was used to determine the relationships between the proactive scale and the ’Big Five‘ personality domains: neuroticism, extraversion, openness, agreeableness, and conscientiousness. In a third sample of 148 MBA students, we assessed the proactive scale's relationships with three personality traits and three criterion measures. Consistent with hypotheses, scores on the proactive scale correlated with need for achievement, need for dominance, and independent measures of the nature of subjects' extracurricular and civic activities, the nature of their major personal achievements, and peer nominations of transformational leaders. We discuss the potential of the proactive construct to enhance our understanding of, and ability to predict, a wide range of behaviors.