This chapter focuses on treaty committees that share interpretative functions with adjudicative bodies. The author explores whether, and to what extent, joint interpretative commissions/committees are in fact signs of convergence between international investment law and international trade law. The author addresses convergence through the following four dimensions: spatial, temporal, ideological and functional. She concludes that the ideological dimension demonstrates a deeper convergence than can be seen from the space and time perspectives, namely the introduction of a new epistemic community into the field of international investment. Furthermore, the functional dimension shows lasting similarities and differences between the fields. Nevertheless, deeper analysis shows up complexity in reconciling states’ dual role as both respondents and interpreters in pending proceedings, and this is where convergence meets resistance.