This section introduces the concept of "Blue Carbon", which refers to the carbon captured and stored by coastal ecosystems like mangrove forests, saltwater marshes, and seagrass meadows. These ecosystems are highly efficient at sequestering carbon from the atmosphere in their plant biomass and in the carbon-rich sediments below the surface. Coastal Blue Carbon ecosystems store much higher amounts of carbon than typical terrestrial forests. The section establishes the global importance of Blue Carbon and sets the stage for discussing projects aimed at conserving coastal ecosystems for their climate change mitigation value.