Book excerpt: Trade negotiations occur through time and between the governments of many countries. An important issue is thus whether the value of concessions that a government wins in a current negotiation may be eroded in a future bilateral negotiation to which it is not party. In the absence of rules that govern the bilateral negotiation, we first show that the potential for opportunistic bilateral agreements is indeed severe. We next identify rules of negotiation that serve to protect the welfare of governments that are not participating in the bilateral negotiation. The reciprocal market access' rule ensures that the market access of a non-participating country is unaltered, and we show that this rule eliminates the potential for opportunistic bilateral negotiations. This rule, however, has practical limitations, and so we next consider the negotiation rules that are prominent in GATT practice and discussion. Our main finding is that the two central rules of GATT -- non-discrimination (MFN) and reciprocity -- effectively mimic the reciprocal market access rule, and therefore offer a practical means through which to protect non-participant welfare and thereby eliminate the potential for opportunistic bilateral negotiations.