Income tax law in general treats a company as a separate taxable unit, reflecting an application of the traditional separate entity doctrine. However, the rise of corporate groups in the last century poses a serious challenge to the doctrine and demands a paradigm shift. The tax consolidation regime is an increasingly common response of the tax law to the challenge, representing an application of the enterprise doctrine under which a corporate group is treated as one single taxable unit. This book aims to improve the understanding of the design and implementation of consolidation regimes by undertaking a comparative study of the regimes in eight countries, namely Australia, France, Italy, Japan, the Netherlands, New Zealand, Spain and the United States. These eight countries are all the countries in the world that, by the end of 2009, have introduced a consolidation regime in their income tax systems. This book analyses and compares alternative policy options adopted in the eight countries for ten key structural elements of a consolidation regime, with the intention of searching for a model regime. The comparative analysis also aims to answer the following tax policy question: does a stronger application of the enterprise doctrine necessarily imply a better consolidation regime on policy grounds? This book provides the first comprehensive comparative analysis of the consolidation regimes in the eight countries. The findings of this study should be useful for tax policy makers to design a new consolidation regime, as well as to refine existing consolidation regimes. I am forever indebted to Richard Vann, without whose mentorship and inspiration this book would never have been completed. My research interest in consolidation regimes was inspired by a lecture delivered by Peter Harris, to whom I acknowledge my sincere gratitude. I am deeply grateful for the critiques and comments of Cynthia Coleman and Daniel Ho on earlier drafts of the book.