The term “blue carbon” is still rather new, having been coined in 2009. However, the blue carbon concept and the role of blue carbon stored in shallow coastal ecosystems, as part of nature-based or green infrastructure, in mitigating climate change and providing other ecosystems services, such as disaster risk reduction, infrastructure resilience, erosion control, and land formation, have attracted the interest of many people worldwide. In this chapter, we first summarize the current status of blue carbon initiatives, including for carbon offsetting, worldwide. Then, we review three blue carbon offset credit projects that have already been implemented in Japan: (1) the blue carbon offset crediting projects of (1) Yokohama City, the first in the world; (2) Fukuoka City, the second such project in Japan; and (3) the first Japanese national governmental demonstration project. Finally, we discuss the need to accelerate the development of blue carbon offset credit projects and related initiatives in the future.