This paper considers the role that contract doctrine should play in facilitating optimal investment in contractual relationships. All contracts are incomplete in the sense that they do not specify the optimal actions for the buyer and seller in every future contingency. This incompleteness can lead to both under and over-investment in resources specifically targeted to the needs of the other contracting party. To solve these investment problems, economists and legal scholars have looked to complicated contractual solutions and the ownership of assets. This Article offers another solution: contract doctrine. Specifically, we propose a contractual default rule applicable to all contract interpretation, gap-filling, and good faith inquiries (a relationship-specific investment, or RSI default) that accounts for the renegotiation position of contracting parties. Because contractual default rules form the backdrop against which parties renegotiate, the RSI default allocates bargaining power to one party or the other in much the same manner as does ownership. The RSI default favors the contracting party making an RSI, while at the same time minimizing potential problems of over-investment through a notice requirement. We also offer some preliminary thoughts on the problem of two-sided RSIs
