This chapter focuses on three key EU justice and home affairs agencies: The European Union Agency for Law Enforcement Cooperation (Europol), The European Union Agency for Criminal Justice Cooperation (Eurojust), and the European Border and Coast Guard Agency (Frontex). This chapter analyses their origin, structure, delegation of powers, and main activities. Europol specializes in the fight against international crime and terrorism, Eurojust supports cooperation in criminal matters, and Frontex focuses on protecting the EU’s external borders. This chapter highlights the differences in their mandates, organizational structure, and operational capabilities. Key takeaways include the importance of these agencies to EU security, their role in responding to security challenges such as Russia’s invasion of Ukraine, and their contribution to protecting European citizens. This chapter also examines issues of democratic accountability, control mechanisms, and cooperation between agencies and member states.