Meissen, U.U.MeissenVoisard, A.A.Voisard2022-03-042022-03-042010https://publica.fraunhofer.de/handle/publica/22425710.4018/978-1-61520-987-3.ch008The deployment of Early Warning Systems (EWS) and Alerting Technologies (AT) is one of the best measures for improved disaster prevention and mitigation. With the evolution of Information and Communication Technologies (ICT), we face new opportunities as well as new challenges for improving classical warning processes. This chapter concentrates on the main aspects of existing early warning systems and alerting technologies. Beginning with the definition and classifications in this field, we describe general approaches, representative systems, and interoperability aspects of EWS. Furthermore, we introduce a list of criteria for evaluating and comparing existing systems. It is worth noting that the deployment of an operational EWS is a complex challenge and remains a young field of research. This is due to many reasons, ranging from the political to the technical. The most critical issues regarding efficient alerting are described in this chapter, along with areas for fut ure research.en004book article