This module concerns global biodiversity, what we understand by it and why it is in crisis, and current efforts to conserve and manage it. We begin with an appraisal of different values of diversity at scales from genetic to species, communities and ecosystems. We then consider the causes and consequences of losing biodiversity, the nature and scale of its loss, countermeasures at global, national and local scales, and the costs we may face in replacing services that depend on biodiversity. During the second half of the module, we take a community ecology approach, focusing on interactions between species, rather than species per se. We look at networks of interactions, and consider how they have been used to address practical issues in conservation. Finally, we consider global impacts on ecosystems, how they interact with one another, and how we might mitigate their impacts. The module seeks to engage discussion and debate,and inform opinion, on biodiversity and conservation.