Building on the literatures on technoscientific promising and social license to operate (SLO), this chapter draws on examples from the nuclear sector and its latest promise, the small modular reactors (SMRs), to examine how the construction of technoscientific promises—often at national and even international level—manifests itself at the local level, if and when the promises are materialized at the local level in the form of concrete projects. The chapter calls for greater collaboration between the scholarly communities working on the interrelated topics of SLO and technoscientific promises. To illustrate the key challenges associated with the interaction between geographically bound SLO and the technologically bound technoscientific promises, this chapter analyses the promise of SMRs. It does so by combining two conceptual frameworks: one defining legitimacy and credibility as the key preconditions for a powerful technoscientific promise, as suggested by Joly and Le Renard, and another relying on the “diamond” or “arrowhead” model of SLO developed by Boutilier and Thomson. The chapter highlights the key features that condition the attempts of SMR projects to obtain a local-level SLO: (1) the long and complex history of the nuclear sector and its earlier promises; (2) the multiple roles of the state as an owner, promoter, and regulator of nuclear projects; and (3) the resulting complex trust-mistrust relations between and among citizens, state bodies (including especially the regulator), the private industry, and experts. The chapter concludes by emphasizing the need for mistrustful vigilance to ensure alignment among technoscientific promises, SLO, and societal values across levels of governance. Further collaboration is needed between the two scholarly communities to generate sufficient conceptual coherence to enable the interaction between the spatially bound SLO and technologically bound technoscientific promises.