European Union law (historically called European Community law) is a body of treaties, law and court judgements which operates alongside the legal systems of the European Union's member states. It has direct effect within the EU's member states and, where conflict occurs, takes precedence over national law.
The primary source of EU law is the EU's treaties. These are power-giving treaties which set broad policy goals and establish institutions that, amongst other things, can enact legislation in order to achieve those goals. The legislative acts of the EU come in two forms: regulations and directives. Regulations become law in all member states the moment they come into force, without the requirement for any implementing measures, and automatically override conflicting domestic provisions. Directives require member states to achieve a certain result while leaving them discretion as to how to achieve the result. The details of how they are to be implemented are left to member states.
EU legislation derives from decisions taken at the EU level, yet implementation largely occurs at a national level. The principle of uniformity is therefore a central theme in all decisions by the European Court of Justice, which aims to ensure the application and interpretation of EU laws does not differ between member states.