All of the mega-regionals recently concluded or currently negotiated are envisioned or at least highly likely to, among other subjects, provide for a regulatory framework on foreign investments. Against this background this contribution takes a closer look at some of the specific aspects of interactions between these investment chapters and the in principle by now already traditional treaty-making through the conclusion of bilateral investment treaties (BITs). The first section addresses the factual background and some of the underlying expectations shaping the present discussion on the relationship between investment chapters in megaregionals and BITs. In the second part an attempt will be made to systemize the various potential connections based on the identification of two main dimensions of interaction between mega-regionals and BITs. Finally, the contribution will provide a kind of bird's-eye view and some tentative conclusions on the expected consequences of these interactions for the future development of-and scholarly research on-international investment law as a whole.