There is a recognized need to incorporate sustainability considerations in infrastructure projects delivered through public–private partnerships (PPPs). The aim of this study is to explore how such incorporation can be encouraged. The research is based on a documentary analysis of 25 Flemish PPP infrastructure projects and two follow-up single-case studies. The findings show that sustainability considerations currently play only a limited role, and that the social dimensions of sustainability are largely neglected. It seems likely that this neglect is due to the difficulties encountered in formulating measurable social sustainability criteria. Based on case studies, several governance instruments are presented that might stimulate more consideration for sustainability. This study should, therefore, be of value to practitioners who wish to procure sustainable PPP projects. However, it must be noted that a “strong” sustainability perspective seems inherently incompatible with the contractual PPP project structure, which requires measurable and enforceable performance indicators.