A state-of-art assessment of existing monitoring/early warning systems (EWS) organized according to type of environmental threats is presented. This report focuses on: air quality, wildland fires, nuclear and chemical accidents, geological hazards (earthquakes, tsunamis, volcanic eruptions, landslides), hydro-meteorological hazards (desertification, droughts, floods, impact of climate variability, severe weather, storms, and tropical cyclones), epidemics and food security. Current gaps and needs in EWS are also identified and discussed. Chapter 1 introduces the basic concepts of early warning systems; Chapter 2 introduces the role of earth observation for disasters and environment; Chapter 3 focuses on the existing early warning/monitoring systems; and Chapter 4 presents a global multi-hazard approach to early warning.