The law of restitution is commonly described in terms of a unifying principle of 'unjust enrichment at the plaintiff's expense'. Jackman challenges that view, revealing that much of the law of restitution does not concern cases where the defendant has been 'enriched' or where the plaintiff has suffered 'expense'. Demonstrating that there are several distinct concepts of 'injustice' at stake, he then identifies three fundamentally distinct categories of legal thought in this area: the reversal of non-voluntary transactions the fulfilment of non-contractual promises and the protection of the private legal facilities of proprietary rights and fiduciary relationships.In so doing, the author highlights the central and disparate principles of restitution so often masked by the concern for uniformity.