Proactive behavior at work is about making things happen. It involves self-initiated, anticipatory action aimed at changing either the situation or oneself. Examples include taking charge to improve work methods, proactive problem solving, using personal initiative, making i-deals, and proactive feedback seeking. In this chapter, we define proactive behavior and distinguish it from related concepts. We also identify higher-order categories of proactivity in the work place. We then summarize a model of the antecedents and outcomes of proactive behavior, as well as moderators of its effects on performance and other outcomes. We argue a review of this topic is timely given both academic developments and technological and social change occurring within the work place.