Margin of appreciation
Margin of Appreciation is a concept the European Court of Human Rights has developed when considering whether a member state of the European Convention on Human Rights has breached the convention. The margin of appreciation doctrine allows the court to take into account the fact that the Convention will be interpreted differently in different member states. Judges are obliged to take into account the cultural, historic and philosophical differences between Strasbourg and the nation in question.  The margin of appreciation is remotely similar in concept to but different from subsidiarity.
The doctrine was used for the first time in the case Handyside v. United Kingdom , which concerned the publication of a book aimed at school children, a chapter of which discussed sexual behaviour in explicit terms. It was published successfully in other signatory states. The ECHR were willing to allow a limitation of freedom of expression in the interests of the protection of public morals.
Margin of appreciation is the word-for-word English translation of the French phrase "marge d'appréciation", a concept used in a number of courts in Europe, among them the European Court of Human Rights and the European Union courts in Luxembourg. It means, roughly, the range of discretion.
The European Union courts, which are the General Court (previously known as the Court of First Instance) and the European Court of Justice, use French as the "language of the court". All decisions are drafted in French and then translated to the appropriate other EU languages. In a number of cases, the courts have had to decide the "marge d'appréciation" of the European Union executive, which is the European Commission. In particular, the concept of "marge d'appréciation" has been used in competition cases. The Commission may bar large company mergers, or fine companies engaged in cartels or abuse of dominance. On occasion companies appeal the Commission decisions to the courts. Sometimes the court decisions have taken note of range of discretion of the Commission. The court has said that the Commission has some discretion—its "marge d'appréciation"—over deciding facts and making an economic analysis. The court has said the Commission can be reversed only if it makes a "manifest error of judgement".
In practice, it has sometimes used both these phrases as it has clipped the wings of the Commission. The best examples of this are three cases decided by the Court of First Instance (now known as the General Court) in 2002, the Airtours/First Choice case, the Tetra Laval-Sidel case, and the Schneider-Legrand case. The decisions, in which the Commission decisions were overturned, are available in French, English and other languages on the court's official website.
For more controversial topics, such as cases involving bioethics or assisted reproduction, the Court recognises that to make a definitive stance for all contracting States would mean ignoring the social and cultural values which lie behind the decisions of national legislatures.
“Where, however, there is no consensus within the Member States of the Council of Europe, either as to the relative importance of the interest at stake or as to how best to protect it, the margin will be wider. This is particularly so where the case raises complex issues and choices of social strategy: the authorities' direct knowledge of their society and its needs means that they are in principle better placed than the international judge to appreciate what is in the public interest… There will also usually be a wide margin accorded if the State is required to strike a balance between competing private and public interests or Convention rights.” - Dickson v. United Kingdom