How can I as an international lawyer, conscious that international law is deeply implicated in today's global injustices and that the course of history will not be changed by any grand legal design, practice law responsibly? Taking as a point of departure my own desire not to seek comfort in the formulation of a critique of law, but to aspire to a responsible practice, I consult two quite different bodies of work: first, critical theory of law and second, recent scholarship on international law that argues a practice guided by ethics may enhance the legitimacy of international law. I turn then to my own practice of international economic law focusing on my occasional role as legal expert on the so-called megaregionals the EU aims to conclude with Canada and the United States. I propose that the debate on international economic law lacks an investigation into the role of law in shaping political economy; that this lack can be explained by the compartmentalization of expertise which leads to justification gaps with respect to projects such as the megaregionals. One way lawyers can assume responsibility is to work on closing these gaps even if it means leaving the ‘inside’ of the legal discipline. Finally, I suggest that a responsible legal practice of social change might follow Roberto Unger's call for institutional imagination. Maybe I can satisfy my wish for a transformative practice by joining forces with friends in experimenting with institutions, hoping to build an alternative political economy.