An entrepreneurial mindset helps innovators find, interpret, evaluate, and pursue opportunities for their innovations. It is a concept having multiple definitions and contradictions variously focused on individual traits, behaviors, attitudes, or beliefs. Robinson claimed that across the various definitions of an entrepreneurial mindset there was little theoretical grounding to be found. To address this shortcoming, this essay describes Social Identity Theory, and its close cousin, Self-Categorization Theory, which have gained significant traction in psychology and sociology, as theoretical foundations for understanding and developing an entrepreneurial mindset. Social identity is a psychological construct describing individuals' perceptions and values of belonging to a particular social group--in this case, affiliating with those identifying themselves as entrepreneurs. The argument put forth here is that a crucial aspect of developing an entrepreneurial mindset in engineering students involves helping them identify as entrepreneurs.