This chapter deals with the principle of proportionality, a specific argumentation technique in constitutional law developed by the courts and scholars in the Federal Republic of Germany in the second half of the twentieth century. This principle eventually gained great significance in constitutional laws of a number of countries.

Although the main function of the principle of proportionality in constitutional law is to determine whether or not a certain restriction of fundamental rights goes beyond the necessary scope and thus whether the standard of fundamental rights is being arbitrarily reduced, this principle simultaneously represents an important instrument for the harmonisation of conflicting constitutional principles and values. Three questions (also denoted as subtests) are traditionally asked as part of the proportionality analysis, specifically:

• 1) whether the relevant regulation limiting a fundamental right is suitable to attain a legitimate objective;

• 2) whether the regulation is necessary, i.e. whether or not it goes beyond what is necessary to attain the relevant legitimate objective and

• 3) whether a balance has been found among the fundamental rights and public interests.

The following figure describes questions asked by the competent public authority (whether it is a legislative, an executive or a judicial body). If all three questions are answered in the affirmative, we can conclude that the given act (decision or legal regulation) is proportionate.

So far, scholarly literature has not paid much attention to the question of how the principle of proportionality contributes to the unification of law. The objective of this chapter will therefore be to point out the potential of the proportionality principle in terms of integration of the law. I shall describe this potential against the backdrop of doctrinal debates regarding the application of the principle of proportionality because, in my opinion, the doctrinal approach is closely related to how this principle is applied in practice. I believe that the significance of this integration potential on the part of the principle of proportionality lies in the fact that it represents an optimisation tool, i.e. that it makes it possible to harmonise conflicting rights and public interests in an environment characterised by the aforementioned value pluralism.