Legal frameworks have an enormous influence on the concrete choice of legal form, especially in (multinational) groups of companies. For example, tax regulations and accounting standards directly influence the legal enterprise’s structure, including the shareholding structures. However, the tax burden must not be understood as a static or a fixed quantity determined in advance. This is because the design or choice of companies’ legal form can also be used as a tool to gain competitive advantages and optimise the tax burden or after-tax profit. Accordingly, the tax-optimising choice of legal form can be used as an instrument for tax planning and internal financing (reduction of tax payments and optimisation of the group tax rate). Therefore, for groups of companies and multinationals, the question that arises is how and within what limits can they make effective use of the cross-border tax rate differential, particularly through structuring their legal form. However, using cross-border tax advantages may be prevented by the controlled foreign corporation (CFC) taxation, called the Anti Tax Avoidance Directive (ATAD), which was introduced in all EU member states from 1 January 2019 onwards due to European law: Art. 7, 8 of Directive 2016/1164 to combat tax avoidance practices. In multinational companies, there is a tension between the tax-optimising choice of legal form, including the structuring of shareholdings, and CFC taxation. It is important to identify the CFC taxation requirements according to ATAD or the respective member state of residence and to avoid these requirements when structuring individual circumstances or investments. An important finding here is that the factual prerequisites for CFC taxation under ATAD are not aligned with the accounting rules, especially controlling interest and control participation. Finally, from an overall perspective, tax-optimised corporate groups’ structure or the legal architecture is not a static variable but an evolving system composed of tax-optimised sub-systems or subgroup structures. This connection between the choice of legal form, shareholding structure and the legal system, tax planning, and tax optimisation in multinational companies is analysed and evaluated based on the Austrian CFC taxation (Sec. 10a CITA) and the German CFC taxation (Sec. 7 FTTA). Furthermore, the implications for companies and society, and the legislator, are highlighted. The article also deals with the relationship between law and tax planning.