The purpose of this project is to investigate the construction of equal treatment in a legal field that concerns most people i.e. in tax law. Is it possible to formulate general criteria for comparability, and can it be done in a way, which is consistent and controlled? The project is to be completed over a two-year period and will be accounted for in a monograph written in Swedish as well as in articles in Swedish and in English. The monograph will hold two parts. The general part will contain an analysis of the concept of equal treatment in taxation, including a demarcation between the principle of equality in tax matters from other tax law principles. In addition constitutional prerequisites for such equality will be investigated. Subsequently, in the second and more specialized part of the monograph I will analyse the implications and importance of administrative practice, with regard to equal treatment. Furthermore, the second part will hold an inventory and analysis of criteria, which may be relevant to the social construction of comparable cases. Some tentative examples of such criteria are the relations between taxation on the one hand and different lines of trade or business, location, time and standard assessments on the other hand.