Opt-outs in the European Union

In general, the law of the European Union is valid in all of the twenty-seven European Union member states. However, occasionally member states negotiate certain opt-outs from legislation or treaties of the European Union, meaning they do not have to participate in certain policy areas. Currently, three states have such opt-outs: Denmark (two opt-outs), Ireland (two opt-outs) and Poland (one opt-out). The United Kingdom had four opt-outs before leaving the Union.

This is distinct from the enhanced cooperation, a measure introduced in the Treaty of Amsterdam, whereby a minimum of nine member states are allowed to co-operate within the structure of the European Union without involving other member states, after the European Commission and a qualified majority have approved the measure. It is further distinct from Mechanism for Cooperation and Verification and permanent acquis suspensions, whose lifting is conditional on meeting certain benchmarks by the affected member states. It is also distinct from the delayed entrance into some areas of cooperation which new members are experiencing. These areas include the Schengen Agreement and the Eurozone, and the delay can last for many years and even decades.