The agencies of the European Union (formally: Agencies, decentralised independent bodies, corporate bodies and joint undertakings of the European Union and the Euratom) are bodies of the European Union and the Euratom established as juridical persons through secondary EU legislation and tasked with a specific narrow field of work.
They are distinct from:
international law juridical persons established through primary (treaty) legislation, either as an EU institution (the European Central Bank) or an EU body of other type (such as the European Investment Bank Group entities, the European University Institute, the European Stability Mechanism or the Unified Patent Court)
other EU institutions
other EU bodies lacking juridical personality, including the advisory bodies, the independent offices held by a single person (European Ombudsman, European Data Protection Supervisor), and the (non-independent, auxiliary) EU inter-institutional services, regardless whether established through treaty or secondary legislation
the pan-EU organisational forms which are not considered constituent bodies of the EU or the Euratom, regardless whether possessing juridical personality (European Research Infrastructure Consortium, European political party, European political foundation, European grouping of territorial cooperation, Societas Europaea, Societas Cooperativa Europaea) or lacking it (European economic interest grouping)
In contrast to other EU bodies established through secondary legislation, each of more than fifty such entities has its own juridical personality granted by the EU law, recognised across the EU, and in some cases, also across the EEA countries, Switzerland, Serbia, Ukraine, the United Kingdom and Turkey. Nevertheless, in relations with other non-EU third countries, they are in general not recognised as independent entities, thus being considered either parts of the juridical personality of the EU or the Euratom.