The Flood Forecasting and Early Warning in Transboundary River Basins: A Toolkit, produced by the United Nations Economic and Social Commission for Asia and the Pacific (ESCAP) and the Regional Integrated Multi-Hazard Early Warning System (RIMES), is a guide book for building capacity of flood management practitioners in transboundary river basins in the Asia-Pacific region. It provides the know-how of utilizing probabilistic and deterministic modeling frameworks, which integrates meteorological, hydrology and flood forecasting models and accesses real time data and information from multiple sources including earth observation satellites, global/regional hydro-meteorological networks. It highlights how the tools, techniques, and other resources available from RIMES, the International Centre for Water Hazard and Risk Management (ICHARM), International Centre for Integrated Mountain Development (ICIMOD), the Mekong River Commission (MRC), the UNITAR’s Flood FINDER, the World Bank's South Asia Water Initiative (SAWI) can be put to operational use for more effective flood forecasting. It is hoped that the toolkit would be of practical value to the flood forecasting community, technical experts, disaster risk managers and policymakers for enhancing flood early warning systems, especially in transboundary river basins. The toolkit begins by describing the main user groups in flood management and their different information requirements. It then moves on to provide a detailed description of the data, methods and distribution channels available for flood forecasting. The toolkit includes numerous examples on how predictive models are integrated into the wider flood management frameworks. Experiences, challenges and lessons learned from the management of various transboundary river basins are also discussed to provide contextual understanding of flood risks in the Asia-Pacific region.