The current book introduces the methodology of data envelopment analysis (DEA). DEA uses mathematical programming techniques and models to evaluate the performance of peer units (e.g., bank branches, hospitals and schools) in terms of multiple inputs used and multiple outputs produced. DEA examines the resources available to each unit and monitors the "conversion" of these resources (inputs) into the desired outputs. The book gives an overview of the various models from the literature, and the geometric interpretations provided permit the reader to go beyond the mathematics. Various topics are covered relating to important practical considerations. These include dealing with time series data as well as methods for restricting multipliers. The book will thus provide students, researchers and practitioners with a solid understanding of the methodology, its uses and its potential.