What role does social identity play in the transition from employed work to entrepreneurship? It was expected that social identity affects the cognitive processes that, according to the theory of planned behavior (TPB), underlie the formation of entrepreneurial intentions. Focusing on academic scientists' intentions to commercialize research knowledge, we investigated social identity (scientists' group identification with their workplace peers in academia) as a moderator in the TPB model. Our hypotheses were tested in a sample of 488 German scientists. The data revealed that entrepreneurial intentions were predicted by attitude, social norms, and perceived control and that group identification was negatively associated with perceived control. Multi-group structural equation modeling further showed that group identification moderated the TPB-intention link. Scientists with low group identification based their entrepreneurial intentions not so much on social norms and attitudes but on their self-initiative and control beliefs. Among scientists with high group identification, in turn, entrepreneurial intentions were mainly a function of social norms. These results, in sum, illustrate the long-neglected importance of identification with, and social cohesion within, peer groups at the workplace for the transition to entrepreneurship. (Contains 1 figure and 2 tables.)