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, some member states can opt-out from legislation or treaties of the European Union, meaning they do not have to be part in certain policy areas. 
Only three states have such opt-outs: Denmark (two opt-outs), the Republic of Ireland (two opt-outs) and Poland (one opt-out). The United Kingdom had four opt-outs before leaving the Union.