The number of comparative tax law studies is substantial. The available literature on the methodology behind these tax comparisons, however, is rather limited and underdeveloped. This article aims to contribute to the theoretical background of tax comparisons by explicating methodological considerations in a comparative tax research on tax incentives for cross-border donations and relating it to the available methodological literature. Two aspects of tax law make comparative research in tax law a challenging endeavour: its complexity and fast-changing nature. To overcome these issues, this article proposes to divide jurisdictions into a limited number of categories. In this process the different legal levels are analysed systematically, resulting in categories of jurisdictions. Among the jurisdictions in one category, common characteristics are identified. This results in an abstract description of the category. I use the term ‘ideal types’ for these categories. The high level of abstraction in the use of ideal types allows for comparison of tax jurisdictions, without the risk that the comparison gets outdated. An additional advantage of working with ideal types is that the conclusions of the comparison can be applied to all jurisdictions that fit in the ideal type. This increases the generalisability of the conclusions of the comparative tax research.

In today’s global economy, a noticeable trend is that the traditional state-law-centred legal framework is increasingly challenged by self-regulatory private orders. Commercial norms, commercial arbitration and social sanctions at the international level have become important alternatives to national laws, national courts and legal sanctions at the national level. Consisting of transnational commercial norms, both codified and uncodified, and legal norms, both national and international, a plural regime for the governance of transnational commercial transactions has emerged and developed in the past few decades. This article explores the interaction between various kinds of norms in this regime, identifies the effects of this interaction on the governance of transnational commercial transactions and shows the challenges to this interaction at the current stage. The central argument of this article is that the interaction between social and legal norms, namely incorporation and internalisation, and the three effects derived from incorporation and internalisation, namely systematisation, harmonisation and compliance enhancement, are evident at both the national and international levels. In particular, the emergence of codified transnational commercial norms that are positioned in the middle of the continuum between national legal norms and uncodified transnational commercial norms has brought changes to the interaction within the international dimension. Although the development of codified transnational commercial norms faces several challenges at the moment, it can be expected that these norms will play an increasingly important role in the future governance of transnational commercial transactions.