Coastal mapping and shoreline change detection are critical to many applications, including navigation, coastal zone management, coastal environmental protection, and sustainable development. Field surveying and on-site investigation become inevitable to ensure the quality of coastal decision making. To provide innovative tools for governmental agencies to increase efficiency and reduce operation costs, a wireless mobile GIS is developed and applied to on-site decision making for coastal management. This wireless mobile GIS system has three components: a coastal-structure permit subsystem; a shoreline erosion awareness subsystem; and a wireless on-site spatial subsystem. The coastal-structure permit subsystem has been implemented to simulate, in a GIS environment, the decision-making process for granting construction permits for coastal protection structures. The web-based shoreline erosion awareness subsystem has been developed to aid local residents in making land-use decisions. It is implemented both to describe the extent of historic shorelines and previous erosion and to predict future shoreline change due to erosion. The wireless on-site spatial subsystem helps government officials remotely access and update spatial data from field, thus allowing for decision making in real time. This system has been developed in the United States based on the environment at Lake Erie, Ohio.