There are three sources of law within the EU legal system:
'Primary legislation' - the treaties and agreements of similar status
'Secondary legislation' - laws made under the powers established by the treaties
Case law - the accumulated body of legal decisions built up by the European courts
Together, this body of jurisprudence constitutes the acquis communautaire, with which all member states - and aspirant member states - are required to comply with and to render their domestic laws consistent with, under pain of sanctions.