Double non-taxation stemming from hybrid financial instruments and the solutions provided by the OECD and the European Union for tackling such an outcome are the target of this publication. It focuses on the economic and legal features of debt and equity instruments as well as hybrid financial instruments from an interdisciplinary perspective where economics, corporate law, financial accounting law, regulatory law and tax law are present. The different qualification of hybrid financial instruments within and without jurisdictions may lead to double non-taxation across borders, which is one of the main issues of concern to the international tax community.