Article 21 of the OECD Model Tax Convention on Income and on Capital has seldom captured the attention of commentators, perhaps because of its elusive nature and yet Article 21 plays an important role within the system of the tax treaties. Indeed Article 21 has a simple structure as it consists of just an allocation rule (Article 21 § 1) together with a rule on the force of attraction on other income effectively connected to a permanent establishment (Article 21 § 2). Article 21 it also has two essential dimensions that attribute to it a central role in the structure of the Model: the ‘catch-all dimension’, and the ‘third-country dimension’. The ‘catch-all dimension’ is that Article 21 plays a residual role in respect of all the other classes of income regulated by tax treaties and focuses on income ‘other than’ that falling in other treaty rules (the so-called ‘other income’): by taxing the other income Article 21 fills gaps in the structure of the treaty but does not create new taxable situations. The ‘third-country dimension’ is that Article 21 is the only treaty rule that deals expressly with income sourced in third countries (i.e. countries that are neither the treaty residence-country nor the treaty source-country. The combination of these two essential dimensions of Article 21 provides a matrix in which the analysis of Article 21 in this article is divided into two main parts: first, the analysis of other income ‘not dealt with by other articles of the treaty’, i.e. sourced in the SC (section 1); and second, the analysis of other income ‘from sources not expressly mentioned’, i.e. sourced in third countries (section 2).