The Multilateral Instrument (MLI) proposed in OECD BEPS Action 15 will lead to the modification of numerous tax treaties. As tax treaties can have different wording, terminology and structure, a great challenge is to find a proper way to accomplish their modification without distorting the underlying framework or triggering undesirable effects.This book analyses the MLI, which was signed by over seventy jurisdictions on 7 June 2017. The topics covered include: the procedural mechanisms on how the new measures to prevent base erosion and profit shifting (BEPS) will interact with and complement existing tax treaties; the scope of the MLI in order to ascertain which tax treaties and taxes are covered; the interpretation of terms used in the MLI and the relationship between the languages used in the MLI and in the particular tax treaties; the implementation of the minimum standard through the MLI, as well as how states can exercise various options offered by the MLI and reserve the right not to apply certain provisions of the MLI; the legal consequences of the exercise of options and reservations for the other states; the notification procedure through which states declare their choices; and the possibilities and procedure for withdrawal from the obligations entered into upon signing the MLI.Finally, the book discusses whether the mechanism of the MLI can serve as a role model for future changes to the OECD Model Convention.The book incorporates the analyses of leading scholars and practitioners dealing with international tax matters. Critical insights are offered for academics, practitioners, tax officials and judges who deal with or are interested in the field of international taxation.