As constitutional law is being globalized, the quest for a common grammar or 'generic constitutional law' becomes more pressing. That proportionality may be one element of such common grammar is both widely accepted and highly contested. In view of this alarming tension between the triumphant success of proportionality and the severity of criticism, the book engages in an in-depth analysis of this criticism and demonstrate that the objections against the proportionality test are not convincing. The book clarifies and further develops the current theories of proportionality and balancing. While the book is broadly based on Alexy's principles theory, it suggests several modifications to this theory. Examples are taken from the case law of the European Court of Human Rights, the European Court of Justice and various national constitutional courts in order to exemplify the argument and demonstrate its relevance for deciding concrete cases. The book defends proportionality analysis as an instrument located this side of, rather than beyond, constitutionalism. But given the often underestimated capability of instruments like the proportionality test, the limitations of constitutionalism are farther away than it is sometimes considered.