Van Duyn v The Home Office (case 41/74)  ECR 1337.
 The United Kingdom observes that, since Article 189 of the Treaty distinguishes between the effects ascribed to regulations, directives and decisions, it must therefore be presumed that the Council, in issuing a directive rather than making a regulation, must have intended that the directive should have an effect other than that of a regulation and accordingly that the former should not be directly applicable.
 If, however, by virtue of the provisions of Article 189 regulations are directly applicable and, consequently, may by their very nature have direct effects, it does not follow from this that other categories of acts mentioned in that Article can never have similar effects. It would be incompatible with the binding effect attributed to a directive by Article 189 to exclude, in principle, the possibility that the obligation which it imposes may be invoked, by those concerned. In particular, where the Community authorities have, by directive, imposed on Member States the obligation to pursue a particular course of conduct, the useful effect of such an act would be weakened if individuals were prevented from relying on it before their national courts and if the latter were prevented from taking it into consideration as an element of Community law. Article 177, which empowers national courts to refer to the Court questions concerning the validity and interpretation of all acts of the Community institutions, without distinction, implies furthermore that these acts may be invoked by individuals in the national courts. It is necessary to examine, in every case, whether the nature, general scheme and wording of the provision in question are capable of having direct effects on the relations between Member States and individuals.
 By providing that measures taken on grounds of public policy shall be based exclusively on the personal conduct of the individual concerned, Article 3(1) of Directive No 64/221 is intended to limit the discretionary power which national laws generally confer on the authorities responsible for the entry and expulsion of foreign nationals. First, the provision lays down an obligation which is not subject to any exception or condition and which, by its very nature, does not require the intervention of any act on the part either of the institutions of the Community or of Member States. Secondly, because Member States are thereby obliged, in implementing a clause which derogates from one of the fundamental principles of the' Treaty in favour of individuals, not to take account of factors extraneous to personal conduct, legal certainty for the persons concerned requires that they should be able to rely on this obligation, even though it has been laid down in a legislative act which has no automatic direct effect in its entirety.
 If the meaning and exact scope of the provision raise questions of interpretation, these questions can be resolved by the courts, taking into account also the procedure under Article 177 of the Treaty.
 Accordingly, in reply to the second question, Article 3 (1) of Council Directive No 64/221 of 25 February 1964 confers on individuals rights which are enforceable by them in the courts of a Member State and which the national courts must protect.
 By the third question the Court is asked to rule whether Article 48 of the Treaty and Article 3 of Directive No 64/221 must be interpreted as meaning that
'a Member State, in the performance of its duty to base a measure taken on grounds of public policy exclusively on the personal conduct of the individual concerned is entitled to take into account as matters of personal conduct:
(a) the fact that the individual is or has been associated with some body or organization the activities of which the Member State considers contrary to the public good but which are not unlawful in that State;
(b) the fact that the individual intends to take employment in the Member State with such a body or organization it being the case that no restrictions are placed upon nationals of the Member State who wish to take similar employment with such a body or organization.'
 It is necessary, first, to consider whether association with a body or an organization can in itself constitute personal conduct within the meaning of Article 3 of Directive No 64/221. Although a person's past association cannot in general, justify a decision refusing him the right to move freely within the Community, it is nevertheless the case that present association, which reflects participation in the activities of the body or of the organization as well as identification with its aims and its designs, may be considered a voluntary act of the person concerned and, consequently, as part of his personal conduct within the meaning of the provision cited.
 This third question further raises the problem of what importance must be attributed to the fact that the activities of the organization in question, which are considered by the Member State as contrary to the public good are not however prohibited by national law. It should be emphasized that the concept of public policy in the context of the Community and where, in particular, it is used as a justification for derogating from the fundamental principle of freedom of movement for workers, must be interpreted strictly, so that its scope cannot be determined unilaterally by each Member State without being subject to control by the institutions of the Community. Nevertheless the particular circumstances justifying recourse to the concept of public policy may vary from one country to another and from one period to another, and it is therefore necessary in this matter to allow the competent national authorities an area of discretion within the limits imposed by the Treaty.
 It follows from the above that where the competent authorities of a Member State have clearly defined their standpoint as regards the activities of a particular organization and where, considering it to be socially harmful, they have taken administrative measures to counteract these activities, the Member State cannot be required, before it can rely can the concept of public policy, to make such activities unlawful, if recourse to such a measure is not thought appropriate in the circumstances.
 The question raises finally the problem of whether a Member State is entitled, on grounds of public policy, to prevent a national of another Member State from taking up gainful employment within its territory with a body or organization, it being the case that no similar restriction is placed upon its own nationals.
 In this connection, the Treaty, while enshrining the principle of freedom of movement for workers without any discrimination on grounds of nationality, admits, in Article 48(3) limitations justified on grounds of Public policy, public security or public health to the rights derived from this principle. Under the terms of the provision cited above, the right to accept offers of employment actually made, the right to Move freely within the territory of Member States for this purpose, and the right to stay in a Member for the purpose of employment are, among others, all subject to such limitations. Consequently the effect of such limitations) when they apply, is that leave to enter the territory and the right to reside there may be refused to a national of another Member State.
 Furthermore, it is a principle of international law, which the EEC Treaty cannot be assumed to disregard in the relations between Member States, that a State is precluded from refusing its own nationals the right of entry or residence.
[231 It follows that a Member State, for reasons of public policy, can, where it deems it necessary, refuse a national of another Member State the benefit of the principle of freedom of movement for workers in a case where such a national proposes to take up a particular offer of employment even though the Member State does not place a similar restriction upon its own nationals.