Aggressive Tax Planning is an increasing source of concern for many governments. This new OECD report describes the most common types of hybrid mismatch arrangements (i.e. arrangements exploiting differences in the tax treatment of instruments, entities or transfers between two or more countries) and the effects they aim to achieve. It summarises the tax policy issues raised by these arrangements and describes the policy options to address them, with a focus on domestic law rules which deny benefits in the case of hybrid mismatch arrangements and countries’ experiences regarding their application. The report concludes that the same concern that exists in relation to distortions caused by double taxation exists in relation to unintended double non- taxation and recommends a number of actions to be undertaken.