When and why do people engage in different forms of proactive behavior at work? We propose that, as a result of a process of trait activation, employees with different types of self-construal engage in distinct forms of proactive behavior if they work in environments consistent with their self-construals. In an experimental Study 1 (N = 61), we examined the effect of self-construals on proactivity and found that people primed with interdependent self-construals engaged in more work unit-oriented proactive behavior when job interdependence also was manipulated. Priming independent self-construals did not enhance career-oriented proactive behavior, even when we manipulated job autonomy. In a field Study 2 (N = 205), we found that employees with interdependent self-construals working in jobs with high interdependence reported higher work unit commitment and higher work unit-oriented proactive behavior than employees in low interdependent jobs. Employees with independent self-construals working in jobs with high autonomy also exhibited stronger career commitment and more career-oriented proactive behavior than those in jobs with low autonomy. This research offers a theoretical framework to explain how dispositional and situational factors interactively shape people's engagement in different forms of proactive behavior.