In all legal systems of the European Union, the law of contract and the law of tort form the main pillars of the law of obligations. Legal history and comparative law show, however, that it is not possible to get along with these two bodies of legal rules alone, even if their scope of application is generously conceived. For that reason the Study Group on a European Civil Code has decided that it would be essential to draft principles covering those parts of the law of obligations which to some extent lie between the law of contract and the law of tort and which fill the gaps that those areas of the law leave behind. These "gap fillers" include, in addition to the law of unjustified enrichment, the law relating to the unsolicited and voluntary undertaking of another's affairs on the basis of a reasonable ground for intervention. This latter field of law is examined in Benevolent Intervention in Another's Affairs.