Globally, public-private partnerships (PPPs) have increased in popularity as an alternative procurement model for infrastructure development projects. While PPPs have been widely researched and remain subject to extensive debate, the process of PPP institutionalization has been largely overlooked. To address this knowledge gap, we utilize a combination of both Johnson et al.’s (2006) four phases of institutionalization—innovation, local validation, diffusion, and general validation—and Mrak’s (2014) three models of PPP institutionalization—centralized, decentralized, and mixed—to examine the current state of the U.S. PPP market. Using data on 368 U.S. PPP projects from Inframation’s global transactions database, our case analysis indicates America’s PPP institutionalization process is strongly decentralized and currently in a state of diffusion. Our analysis also suggests general validation of PPPs in the U.S. will likely be predicated on shifting to a mixed PPP institutionalization model.