Viewing collaboration as an imperative for public managers, scholars are calling for a better understanding of its origins, prevalence, and impact on organizational performance. The objective of this study is to explore the prevalence and the determinants of collaboration pursued in the course of monitoring government contracts. The theoretical framework proposed in this study explores the effect of several categories of collaboration determinants pertaining to government agencies, contractors, contractual relationships, services, and markets. Data were collected using semi-structured interviews administered to 69 state and local contract managers as well as nonprofit and for-profit contractors in five jurisdictions. Qualitative analysis identifies a variety of collaborative strategies used by agencies seeking vendors’ input and by vendors proposing and negotiating performance monitoring arrangements. Regressions analysing the determinants of collaboration suggest that the latter is more often pursued by nonprofit contractors and vendors with a unique expertise and higher resource dependency. Governments with advanced in-house professional capacity and willingness to collaborate are also more likely to rely on the contractors’ input. Meanwhile, high service measurability, long-term relationships, and dynamic markets reduce the likelihood of collaboration. This study suggests that collaborative performance evaluation presents both challenges and opportunities for effective contract implementation. The responsibilities of monitoring officers appear to extend beyond specifying and enforcing performance standards—they require the skills and motivation to empower contractors and to learn from their input and the professional capacity to evaluate their claims