Murder is an offence under the common law of England and Wales. It is considered the most serious form of homicide, in which one person kills another with the intention to cause either death or serious injury unlawfully. The element of intentionality was originally termed malice aforethought, although it required neither malice nor premeditation. Baker (Glanville Williams Textbook of Criminal Law; London: Sweet & Maxwell, 2015), chapter 14 states that many killings done with a high degree of subjective recklessness were treated as murder from the 12th century right through until the 1974 decision in DPP v Hyam.

Because murder is generally defined in law as an intent to cause serious harm or injury (alone or with others), combined with a death arising from that intention, there are certain circumstances where a death will be treated as murder even if the defendant did not wish to kill the actual victim. This is called "transferred malice", and arises in two common cases:

• The defendant intended serious harm to one or more persons, but an unintended other person dies as a result;
• Several people share an intent to do serious harm, and the victim dies because of the action of any of those involved (for example, if another person goes "further than expected" or performs an unexpectedly lethal action).