How do states allocate joint fish stocks that straddle international boundaries? What factors determine who gets what during international negotiations between fishing states? These questions strike at the heart of the literature on international cooperation, and thus answering them will shed light not simply on international and transboundary fisheries management but also on the general challenges of international cooperation. This paper examines how domestic groups influence negotiators and thus the ultimate terms of international agreements. The research focuses on seven agreements spanning 20 years (signed by Norway and Iceland) for managing four shared fish stocks that straddle national and international waters. The main conclusion suggests that a state with a powerful domestic interest group usually gets a more favorable agreement when negotiating with a state with weaker domestic interest groups.