Functional diversity (FD) defined as the value, range, and abundance of functional traits in a given community or ecosystem is increasingly accepted as a synthetic ecological concept that sheds light on ecosystem functioning. Functional group richness and functional biodiversity indices have been proposed to quantify the FD of a community, or some of its components. The comparative assessment of FD in different ecosystems and for different ecosystem processes would be an invaluable tool for a better and more general understanding of what are the functional roles of biodiversity in the provision of ecosystem services. In this volume we offer a synthesis of the methods used to quantify functional diversity and step by step examples to define functional groups and to estimate functional indices. We also compare communities, and changes of diversity along environmental gradients. All the examples may be reproduce using electronic data files and FDiversity, a free software.