As a transitional zone between aquatic ecosystems and terrestrial ecosystems, wetlands play important roles in water balance, flood conservation, regulation of the local climate, removal of pollutants, provide wildlife habitat and recreational tourism as well as other important functions to maintain the ecological balance of the region. Geographically, wetland includes marine and coastal zones, inland wetlands (such as rivers, riverine floodplains, lakes, peatlands, swamp, marshes, et al.), and man-made wetlands (such as ponds, reservoirs, wastewater treatment, irrigated land, et al.) In this book, we discussed wetlands' ecosystem services. Some wetlands, as water source areas, were studied from a perspective of water resources management; some wetlands, located all over the world, were studied with the relationship of climate change; some wetlands as agricultural use land were researched at a bottom level to exam their fertility; and how wetlands functioned in archaeology. Hydrological models of wetland were also covered.