The EU has its own laws and principles which are laid out in its founding treaties. The body can adopt legislation—which member countries must agree and comply with. These laws are divided into two categories: primary, secondary, and supplementary.
The primary legislation is established by the treaties which are the basis for EU action and decision. The treaties set out the distribution of power and jurisdiction between the union and the member states. Primary law is based on the amendments to EU Treaties, annexed protocols to all treaties, and treaties on member states of the EU who have recently joined.
Secondary legislation is constituted from the treaties principles and comprises of directives and regulations. Secondary sources also include unilateral secondary law, conventions, and agreements with other nations. Unilateral acts are those listed in Article 288 of the TFEU and those not listed, but which are respected communications and recommendations. Conventions and agreements may be exemplified by international agreements, agreements between EU institutions and the agreements between the states.
Supplementary law is not provided for in the treaties, but includes justice case-law, the general principles of law and international law. Supplementary Law allows judges to fill in gaps left by primary and secondary laws. The court is also very inspired by international law when developing new EU laws.
Foster, N. (2008). EU law (1st ed.). Oxford: Oxford University Press.