This introductory paper gives the motivation for the EMF 19 study on technology and climate change policy, an overview of the design of the study, some aggregate model comparison results, and a brief introduction to the rest of this volume. The description of the study design includes the models, regions, and scenarios included in the study. The model comparison results focus on aggregate projections of economic growth, energy use, carbon emissions, fuel choice, and carbon taxes required to control carbon emissions. (C) 2004 Published by Elsevier B.V.