Having identified proportionality as the main tool for limiting constitutional rights, Aharon Barak explores its four components (proper purpose, rational connection, necessity and proportionality stricto sensu) and discusses the relationships between proportionality and reasonableness and between courts and legislation. He goes on to analyse the concept of deference and to consider the main arguments against the use of proportionality (incommensurability and irrationality). Alternatives to proportionality are compared and future developments of proportionality are suggested.