Biological diversity, the variety of living things on Earth, is traditionally viewed as a diversity of taxa, species in particular. But other facets of diversity should be considered to address issues pertaining to evolutionary and ecological processes. The aim of this book is to show the strengths of a functional approach to diversity to improve our understanding of the functioning of ecological systems and their components. The focus is on plants, which aremajor components of these systems, and forwhich the functional approach has led tomajor advances over the last 20 years. This book first presents the rationale for a trait-based approach to functional diversity in the context of comparative plant ecology and agroecology. It then shows how this approach can be used to address a number of highly debated questions in ecology, pertaining to plant responses to their environment, controls on plant community structure, ecosystem properties, and services these deliver to human societies. A specific chapter is devoted to the management of functional diversity and ecological data, which is essential to address efficiently major pending questions in ecology.