Knowledge of habitats and their distribution is crucial for the long-term management and monitoring of protected natural areas, particularly in Sub-Antarctic regions, which are severely affected by climate change and invasions of exotic species. The result of a collaboration between the Ecobio laboratory (CNRS-Université de Rennes), the French Polar Institute and the French Southern and Antarctic Lands collectivity, this book is the first comprehensive guide to the terrestrial habitats of the French Southern Lands, classified as a national nature reserve and listed as a Unesco World Heritage Site. The study model is Ile de la Possession, in the Crozet Islands. Resulting of thirteen years of collecting floristic data and carrying out expert surveys on the island, the book identifies forty-six habitats using a determination key, illustrated description sheets and a pioneering typology. Aimed at scientists, managers and enlightened amateurs, this guide reveals the richness of the Crozet Islands’ flora, its associated fauna and its future prospects. It is therefore an essential tool for the knowledge and sustainable conservation of sub-Antarctic ecosystems.