According to Hans Kelsen, validity is a quality of law, the so-called efficacy is a quality of the actual behaviour of men and not, as linguistic usage seems to sug-gest, of law itself. The statement that law is effective means only that the actual behaviour of men conforms with the legal norms.The starting point of this essay is Kelsen’s paradoxical thesis, according to which efficacy is not a property of norms, but a property of behaviour. But what exactly is meant by the statement that behaviour conforms with norms? Is there such a thing as efficacy without conformity? How, then, do norms affect behav-iour? The author investigates the many relationships between norm and action and, using Max Weber’s criteria of the rationality (Rationalität) of social action, distin-guishes four types of rule-responsive behaviour .