Most research on organizational negotiations has concentrated on factors that affect negotiating outcomes, given some predefined problem or issue. In contrast, this paper focuses on the institutionalization of negotiations, or the process through which social definitions of negotiating issues, procedures and outcomes emerge and are accepted by participants as legitimate boundaries of negotiation. A two-stage model of the institutionalization process is proposed and a number of factors affecting the process at different stages are discussed. Historical and contemporary evidence from labor relations in the U.S. steel industry is used to illustrate these arguments. The implications of institutionalization for further research on negotiations in organizations are discussed.