Foreword Vulnerability of intertropical littoral areas The coastal zone is of very high importance for human development and human wellbeing. Half of the global urban population lives in the coastal zone, where it has access to both continental and marine ecosystem services and to maritime transport. These urban populations coexist with rural and traditional coastal populations, some of which still possess good traditional ecological knowledge of the coastal ecosystems. Marine biodiversity and favourable environmental conditions sustain fisheries and aquaculture , represent a source of inspiration for humankind and provide numerous opportunities for recreation and tourism. In addition, coastal areas provide nursery functions for juvenile fish and invertebrates, which is important for the fish and crayfish stocks exploited offshore. Located at the interface between marine energy and continental processes , the coastal landscapes are dynamic environments. Nevertheless, the destruction of habitats and the increasing exploitation of the coastal zone represent serious threats to the ecosystems. Moreover, human land use and modifications in the watersheds have strong impacts on the coastal zone primarily by contributing to their pollution and nutrient over-enrichment. Damming and creation of reservoirs upstream also heavily modify the hydrology of the watersheds and often dramatically reduce the delivery of sediments to the coastal zone. In addition to these regional and local anthropogenic impacts, the coastal zone is vulnerable to global change among which sea level rise and climate change are particularly important drivers. Many coastal zones extend along giant faults and subduction zones, which makes them particularly exposed to earthquakes and tsunami hazards. Other forms of natural hazards are caused by hurricanes and cyclones that develop at sea and whose trajectories often hit the coastlines. The question on how to combine the conservation of the highly valuable coastal ecosystems and their sustainable exploitation with the strong socioeconomic development in the coastal zone is a major challenge for humankind in the 21 st century. This requires both a high degree of political will and appropriate governance together with sound scientific knowledge. Hence, many international and national organisations for research and development work in the coastal zone to contribute to the objectives of sustainable development. The French IRD is one of them, as it develops research in tropical and subtropical countries in partnership with their respective national institutions. This thematic issue provides a collection of results that illustrates the involvement of IRD, of its partners, and of other national and international groups working in the field of tropical and subtropical coastal environments.