Excessive use of force by the police or other law enforcement officials may have lethal outcomes. This chapter describes the core law enforcement principles of necessity and proportionality which govern all use of force in law enforcement. Specific consideration is given to the restrictions imposed on the use of firearms and related ammunition and firing modes. Consideration of less-lethal weapons in law enforcement benefits from the expertise of Dr Abi Dymond of Exeter University. The human rights principles of legality, precaution, and accountability for the use of force are also addressed.