The principle of unjust enrichment came into fruition under English law in the last decade. It is now accepted that the four-stage-test "enrichment", "at the expense", "unjust factor" and "no defences" triggers remedies in restitution. Unjust enrichment resembles Civilian unjustified enrichment in many ways. But it also differs considerably in others, just as do French and German unjustified enrichment. The book aims to explain this.