This book is a collaborative monograph on South China Sea seagrass ecosystems, completed jointly by China and multiple Southeast Asian countries, based on underwater survey data collected from 35 sampling stations between 2008 and 2023. It systematically documents 240 species that inhabit seagrass beds in the South China Sea and its surrounding waters, including 14 seagrass species, 123 associated fish species, 99 invertebrates, as well as 4 non-fish vertebrates, such as sea turtles and dugongs. Illustrated with in-situ underwater photographs, each entry covers taxonomic classification, habitat depth, biogeographic distribution, trophic levels, and IUCN Red List status. The book also distinguishes venomous, toxic and traumatogenic species, elaborating their interactions with humans. Against the backdrop of the ongoing degradation of over 60% of seagrass meadows in Southeast Asian, this book fills a global gap in the field documentation of seagrass biota. It serves as a valuable reference for marine researchers and protected area managers, and is also accessible to divers and tourists. It advances conservation and public science outreach for the coastal ecosystems of the South China Sea.