MI5, formally known as the Security Service, is the United Kingdom’s domestic counter-intelligence and security agency. Its primary mission is to protect the UK against threats to national security, such as terrorism, espionage, and cyber attacks. MI5 works closely with other intelligence agencies, law enforcement, and government departments to identify and neutralize security threats. The agency operates mainly within the UK and focuses on preventing attacks, gathering intelligence, and advising the government on security matters. MI5 also plays a role in safeguarding sensitive information and critical infrastructure. It does not have police powers but can request assistance from law enforcement when necessary.