These lecture notes are part of the Handbook of Sustainable Finance (Roncalli, 2025). They provide the basics of biodiversity for students and professionals who want to understand this topic and the key challenges of biodiversity investing. The first three sections cover the definition of biodiversity, ecosystem functions and services, and threats to biodiversity. These correspond to material typically taught in conservation biology courses. The fourth section focuses on measuring biodiversity. Fi nally, the last two sections cover biodiversity governance and regulation, and biodiversity investment approaches