Early warning technologies have greatly benefited from recent advances in communication and information technologies and an improved knowledge on natural hazards. Nevertheless, gaps remain in early warning technologies and capacities, especially in the developing world, and a lot has to be done for the development of a global multi-hazard system. This report introduces the basic concepts of early warning systems and the role of earth observation for disasters and the environment. It focuses on the existing early warning and monitoring systems and identifies operational gaps for slow-onset hazards both in monitoring, communication and response phases to facilitate timely decision-making. The main goal of the assessment is to lay out guidelines for developing a global multi-hazard early warning system.