The expression ‘application of the law’ and its derivative ‘applicability of the law’ as well as the expression ‘validity of the law’ have many different meanings in legal theory, which are most often intricately related to each other. The purpose of this study is primarily to distinguish, organise and clarify the ways in which they are understood and to establish and analyse their mutual connections. When considering the expression ‘application of the law’, at least two issues must be generally distinguished: the application of a legal norm to various subjects or circumstances as the relation between the content of such a norm and the situations that it regulates (‘a norm applies to x’) and the application of a legal norm as an act performed on the basis of such a norm in order to carry out some legal actions (‘x applies a norm’). The term ‘legal validity’ seems to be no less complex. For the purpose of this study, I will only distinguish two most common meanings. First, validity understood as the membership to the legal system means that a norm is valid if it meets the conditions for belonging to the system. Second, validity understood as the applicability means that a norm is valid if its application and observance are obligatory in compliance with another norm being a metanorm to the former one. In an attempt to establish the relations between various concepts of application of the law and its validity, I intend—in addition to presenting simpler issues—to consider the case of a change in the law consisting in the enactment of a new legal norm and the elimination of the existing one as well as intertemporal problems ensuing in this situation.