© Springer Nature Switzerland AG 2018. This paper presents the design and implementation guidelines of thing federation-as-a-service. The large and growing number of things compliant with the Internet-of-Things (IoT) principles need to be “harnessed” so, that, things’ collective over individual behaviors prevail. A federation gathers necessary things together according to the needs and requirements of the situation that this federation is tasked to handle. Two types of federations exist: planned whose things are all known at design-time and ad-hoc whose things are known after a competitive selection at run-time. In this paper, federations handle situations about emergency services that involve different stakeholders with different backgrounds raising the complexity of ensuring a successful delivery of these services. A system for patient emergency transfer following a tunnel closure is implemented demonstrating the technical doability of thing federation-as-a-service.