When FTX filed for bankruptcy in November 2022, around one million creditors across multiple jurisdictions discovered that assets they believed they owned had been used for speculative trading without their consent. The collapse of Celsius exposed a related problem when its Terms of Use were held to have transferred ownership of deposited assets, leaving hundreds of thousands of customers as unsecured creditors. This book argues that such cases reveal not merely regulatory failures, but fundamental problems of private law. It therefore approaches digital asset custody as a private-law institution, placing private international law at the centre of the analysis and identifying control, rather than possession, as the basis of entitlement in digital assets.

Drawing on seven jurisdictions and the work of the Hague Conference, UNIDROIT and UNCITRAL, the book examines the property foundations of digital asset custody, custodians’ duties and liability, the treatment of client assets in insolvency and the challenges posed by arrangements without a custodian. It develops a functional connecting factor based on the effective locus of control over key management, proposes a Post-Mortem Control Certificate for cross-border succession, and formulates five criteria for a competition-sensitive conflicts architecture. The study concludes with ten principles for a transnational private law of digital asset custody, offering a framework for the institutions currently shaping the legal foundations of this rapidly evolving field.