The identity and existence of a loss-based defence in the law of unjust enrichment is disputed. Widely known as 'passing on', but better identified as 'disimpoverishment', this defence has generated confusion and disagreement across and within England, Australia, Canada and the United States of America. This book seeks to address these problems in three ways. First, by providing a solution to the defence's terminological problems and presenting a coherent picture of the current state of the law. Secondly, by examining whether a defendant's unjust enrichment can be said to have come 'at the expense of' a claimant when a third party has borne the cost of that enrichment. Put another way, whether awards of restitution are, or should be, restricted by the value of a claimant's loss. And finally, by analyzing the reasons in favour of accepting or rejecting a loss-based defence in the law of unjust enrichment. Numerous scholarly textbooks and law journals have devoted space to these issues. This work, however, has tended to focus narrowly on either particular cases or sets of issues. This book seeks to address this deficiency by collating, and providing total coverage of, the controversies and questions pertaining to a loss-based defence in the law of unjust enrichment.This work will be essential reading for anyone interested in the law of restitution, and in its relationship with other areas of private law.

1 Introduction
A. Thematic Outline
B. Chapter Summaries
Part I The Foundations
2 Introduction to the Defence of Disimpoverishment
A. Introduction
B. Questions in Unjust Enrichment
C. Definition
D. Change of Name
E. Another Problem with Pseudonyms
F. Triggering the Defence of Disimpoverishment
G. Assumptions
H. Taxation Agents
I. Burden of Proof
J. Judicial Responses to Disimpoverishment
K. Conclusion
3 Common Law Cases on the Defence of Disimpoverishment
A. Introduction
B. England
C. Australia
D. Canada
E. United States of America
F. Conclusion
4 Statutory Defence of Disimpoverishment
A. Introduction
B. The Defence of Unjust Enrichment
C. Operation of the Unjust Enrichment Defence
D. Recovery for Third Parties of Overpaid VAT
E. Influence of European Jurisprudence
F. Conclusion
Part II 'At The Expense Of' 5 What Might 'At the Expense of 'Mean?
A. Introduction
B. Two Interpretations of 'at the Expense of '
C. The Meaning of 'Loss'
D. Loss and Restitution
E. The Meaning of 'From'
F. Differences between 'From' and 'Loss'
G. Conclusion
H. Addendum
6 What do the Cases say 'At the Expense of 'Means?
A. Introduction
B. Situation 1: 'Gain' Exceeds 'Loss' at the Moment of Receipt
C. Situation 2: 'Gain' Increases After Receipt
D. Conclusion
7 What should 'at the Expense of 'Mean?
A. Introduction
B. The Problem Restated: The Status Quo Ante cannot be Restored
C. Four Conceptions of What 'At the Expense of 'Means
D. Whenever Loss and Gain Do Not Equate
E. 'Gain' Exceeds 'Loss'at the Moment of Receipt
F. 'Gain' Increases After Receipt
G. Conclusion
Part III Other Reasons to Reject or Accept the Defence of Disimpoverishment
8 Other Arguments for Accepting the Defence of Disimpoverishment
A. Introduction
B. False Bases for Accepting the Defence
C. A Legitimate Basis for Rejecting the Defence
D. Conclusion
9 Other Arguments for Rejecting the Defence of Disimpoverishment
A. Introduction
B. False Bases for Rejecting the Defence
C. Potential Bases for Rejecting the Defence
D. Three Reasons for Rejecting the Defence
E. Conclusion
Part IV Third Parties
10 Third Parties
A. Introduction
B. When Can an Action be Brought Against a Claimant?
C. Class Actions
D. Recovery of Overpaid Tax by a Third Party (from the Claimant)
E. Conclusion
11 Conclusion
A. The Problems Restated
B. The Conclusions Reached
C. Restatement

“This whole book is, if one may say so, a splendid example of how to produce a brief, crisp and intelligible argument for a point of legal principle...a splendid addition to the restitution lawyer's bookshelf: if it is not on it, then it should be.” –  Andrew Tettenborn, L.Q.R. 123(OCT), 674-676

“Rush gives a fair and accurate account of all the relevant case law and legislation, and makes some excellent points along the way,...The courts are not alone in finding three-party problems difficult: the rest of us find them difficult too. Understanding them takes time, patience and a clear head. Michael Rush evidently has these qualities and we should be grateful to him for the care with which he has unpicked a notoriously tricky and knotted-up set of problems. I learnt much from reading and thinking about his book and would certainly recommend it to anyone with an interest in the topic.” –  Charles Mitchell, King's Law Journal, Vol 19:2

“This book provides a thorough and well-reasoned exposition of the defence of disimprovishment and, as such, is a welcome companion to the works on unjust enrichment which have preceded it.” –  Anthony Lo Surdo, Australian Banking and Finance Law Bulletin, Vol 22, No 10

“...the detailed case analysis and consideration of one of the key elements necessary to make out a claim in unjust enrichment will ensure that this book is useful...Dr Rush should be commended.” –  Mark Costellov, Sydney Law Review, Volume 29, Number 2

“Dr Rush is to be congratulated on what is an easily accessible work on a very challenging subject.” –  Jessica Palmer, New Zealand Law Journal