The Southern Reach is a fictional area in the novel trilogy by Jeff VanderMeer, starting with "Annihilation." It is characterized by a mysterious and rapidly changing environment, known as Area X, which is cut off from the rest of the world. The Southern Reach is the government agency tasked with investigating this strange region and its bizarre phenomena. The trilogy explores themes of nature, identity, and the unknown through the experiences of various expeditions sent into Area X. Each book delves deeper into the psychological and physical transformations that occur within this enigmatic landscape, raising questions about humanity's relationship with the environment and the limits of understanding.