Private Law Theory

ABSTRACT
‘Mutual trust’ has advanced to one of the most fundamental principles of judicial cooperation in civil and commercial matters and as such of both European civil procedural law and European private international law. In a first step after the Treaty of Amsterdam 1999 mutual trust has established itself as an explanatory and interpretative principle in and for the relevant secondary law, not only for the procedural law on the cooperation in civil and commercial matters, but for all areas of judicial cooperation within the EU, including criminal and asylum matters. In a second step and in light of Article 2 TEU in particular, newly laid down by the Treaty of Lisbon 2009, the European Court of Justice has unfolded mutual trust to a powerful implicit and overarching principle of primary EU law in order to further pursue the EU’s ‘raison d’être’ – integration. Thus, mutual trust must today be conceived as an integral element of the EU’s ‘constitutional identity’. On a doctrinal level, trust in – and residual control of – foreign judicial and legal acts as a condition for integrating foreign elements in one’s own administration of justice, including foreign law (‘trust management’), offers itself as a theory for private international law in its entirety, in particular in regard to its procedural areas. It is the purpose of this Chapter to summarise briefly this remarkable history of mutual trust and to sketch its far-reaching impact today.

Weller, Matthias, Mutual Trust (June 3, 2026).