If associated enterprises make or impose special conditions in their controlled transactions which differ from those independent enterprises would have made, the arm's length principle may authorize a profit adjustment. Such special conditions will not necessarily only be the price conditions, but may also include any other conditions. Hence, associated enterprises may not only value or price their transactions differently from independent enterprises, but may also structure them differently, and even enter into transactions independent enterprises would not contemplate undertaking at all. The OECD has nevertheless recommended its Member countries as a general rule to adjust only price conditions and other valuation elements of controlled transactions based on the arm's length principle. This general rule is sometimes referred to as the "as-structured principle". The first main issue examined in this thesis is the obligation under the as-structured principle to recognize the controlled transaction actually undertaken by the associated enterprises as it has been structured by them. The OECD, however, has identified two circumstances in which the arm's length principle authorizes domestic tax administrations to restructure controlled transactions. These are (i) where the economic substance of the transaction differs from its form and (ii) where the transaction is commercially irrational and its structure practically impedes the determination of an appropriate transfer price. The second main issue examined in this thesis is the authority to restructure controlled transactions based on the arm's length principle. The common theme of the two main issues can be formulated as the question of how broad the authority is that the arm's length principle grants to domestic tax administrations. This study, thus, examines the outer limits of the adjustment authority granted by the arm's length principle. It examines these issues in the light of Article 9(1) of the OECD Model Tax Convention, as interpreted, in particular, by the OECD Transfer Pricing Guidelines for Multinational Enterprises and Tax Administrations. The thesis also analyses relevant domestic law material, especially from Canada, Norway, and the United States, but also from, inter alia, Australia, Denmark, Germany, the Netherlands, Sweden and the United Kingdom.