How and why start-ups become international is still a relevant question in the current literature. This chapter intends to answer both questions by incorporating the notions of institutional entrepreneurship. The study uses a comparative case study of two start-up firms based in Mexico, which recently became international. The analysis of both cases revealed the importance of the role of the firms’ owners. Moreover, it became clear that both owners created and transformed organisational institutions that allowed the firms to become international. The study takes into consideration a multilevel perspective, which analyses both cases at the micro, meso, and macro institutional levels. This chapter intends to contribute to the entrepreneurial and institutional entrepreneurship bodies of literature.