»The Principle of Proportionality in Taxation. A Research on German Constitutional and Tax Law, and Its Application to Taiwanese Cases« The Taiwanese reception of proportionality principle, particularly in the field of tax law, has been unduly general and superficial. Therefore, based on proportionality principle, this research adopts a holistic approach to examine and distinguish various tax law norm groups i.e. fiscal purpose norms, control norms, redistribution norms, simplification purpose norms, and enforcement norms. The refined and clarified tax law norm groups may serve as a model for Taiwanese constitutional law and tax law's further research.