The ECJ has applied fundamental rights and the principle of proportionality for decades. This book tries to elucidate the Court's approach to these fundamental tenets of Community law. It starts with establishing a firm theoretical foundation. Then, the book analyzes the case law of the ECJ and other constitutional courts to find out which method courts actually apply. Next, it is discussed why the courts follow a particular approach. Then, it is considered whether the approach fulfils constitutional requirements. Finally, a rationalizing model of balancing is developed. The book is useful for the practitioner as well as for the researcher. It does not present a mere summary of the Court's case law but a systematization of the underlying rationales.