Carter B. Casady

The study investigates how contractual and relational governance influence partner behaviors and promote sustainability performance of infrastructure public‐private partnerships (PPPs). Survey data from 217 Chinese PPP projects were analyzed using partial least squares structural equation modeling. This study found that both contractual and relational governance have positive effects on PPP sustainability, with contractual governance having a stronger impact. Contractual governance complements relational governance in promoting cooperative behavior, but relational governance does not amplify the effect of contractual governance on opportunistic behavior. The findings highlight the role of contracts in curbing opportunism and promoting collaboration via multiple functions of control, coordination, and adaption, while also revealing the limitations of relational approaches in the context of government‐business relationships and performance ambiguity. This study contributes to the PPP governance literature by uncovering the individual and interactive effects of contractual and relational governance on the economic, social, and environmental aspects of PPP sustainability.