Malice aforethought is the "premeditation" or "predetermination" (with malice) required as an element of some crimes in some jurisdictions and a unique element for first-degree or aggravated murder in a few. Insofar as the term is still in use, it has a technical meaning that has changed substantially over time.

Malice aforethought is a direct translation of the Law French term malice prépensée, so the adjective follows the noun as in French.

This [malice aforethought] is the grand criterion, which now distinguishes murder from other killing: and this malice prepense, malitia praecogitata, is not so properly spite or malevolence to the deceased in particular, as any evil design in general; the dictate of a wicked, depraved, and malignant heart: un disposition a faire un male chose [an inclination to do an evil thing]: and it may be either express or implied in law.

Malice aforethought was not an element of murder in early medieval English law cases. Both self-defence killings and death by misadventure were treated as murder by juries. Although pardons for self-defence became common after the Statute of Gloucester was passed in 1278, the jury in a 14th-century case still found that a self-defence killing was felonious.

In the 12th century, any death by misadventure without a "presentment of Englishry" was sufficient for a jury finding of murder, even in cases where there was no suspect and the victim's identity was unknown. The murder fine was levied in these cases under the Laws of Henry I until 1267, when the fine for death by misadventure was abolished by the Statute of Marlborough during the baronial reform movement. The primary meaning of murdurum continued to be murder fine until the fine was abolished by the Engleschrie Act 1340 (14 Edw. 3 Stat. 1. c. 4).

The first statutory mention of malice aforethought dates to the reign of Richard II in 1389. In 1390, Parliament defined murder as "death of a man slain by await, assault, or malice prepensed". Henceforth, juries were instructed to consider whether a felony had been committed with malice aforethought. A 1403 jury instruction recorded in a 16th-century manuscript written by Edward Stillingfleet reads:

Also you will inquire about all sorts of homicides both of those who lie in wait through malice aforethought [par malice devant pourpense] in the peace of homes and other places [and who] murder people and of those who slay men through a hot-blooded mêlée [chaude melle].^{[full citation needed]}

Some scholars have identified concepts from Anglo-Saxon law as the origin for malice aforethought, but the connection is disputed. The Anglo-Saxon legal concept of forsteal included lying in wait and ambush, but it remains unclear whether or not premeditation or intent were requirements for murder during this early period. It has been argued that forsteal became agwait purpense in medieval English law, which was also called agwait premeditatus in Latin.