Malcolm III (Middle Irish: Máel Coluim mac Donnchada; Scottish Gaelic: Maol Chaluim mac Dhonnchaidh; c. 1031–13 November 1093) was King of Alba from 1058 to 1093. He was later nicknamed "Canmore" (Scottish Gaelic: ceann mòr, lit. 'big head', understood as "great chief"). Malcolm's long reign of 35 years preceded the beginning of the Scoto-Norman age. Henry I of England and Eustace III, Count of Boulogne were his sons-in-law, making him the maternal grandfather of Empress Matilda, William Adelin and Matilda I, Countess of Boulogne. All three of them were prominent in English politics during the 12th century.

Malcolm's kingdom did not extend over the full territory of modern Scotland: many of the islands and the land north of the River Oykel were Scandinavian, and south of the Firth of Forth there were numerous independent or semi-independent realms, including the kingdom of Strathclyde and Bamburgh, and it is not certain what if any power the Scots exerted there on Malcolm's accession. Throughout his reign, Malcolm III led at least five invasions into English territory. One of Malcolm's primary achievements was to secure the position of the lineage that ruled Scotland until the late thirteenth century, although his role as founder of a dynasty has more to do with the propaganda of his descendants than with history. He appears as a major character in William Shakespeare's Macbeth, while his second wife, Margaret, was canonised as a saint in the thirteenth century.

Malcolm's father Duncan I became king in late 1034, on the death of Malcolm II, Duncan's maternal grandfather and Malcolm's great-grandfather. One Scottish king-list gives Malcolm's mother the name Suthen (Suthain), a Gaelic name; John of Fordun states that Malcolm's mother was a "blood relative" (consanguinea) of the Danish earl Siward, though this may be a late attempt to deepen the Scottish royal family's links to the earldom of Northampton (of which Siward was regarded as founder). Later tradition, attested by the fifteenth century, makes Malcolm's mother the daughter of the miller of Forteviot and presents Malcolm as a bastard.

Duncan's reign ended violently; he was killed in battle in Moray on 15 August 1040, by a force under the command of Macbeth. Duncan may have been young at the time of his death, and Malcolm and his brother Donald were probably children. Malcolm's paternal grandfather was killed in battle in 1045, possibly as part of some continuing conflict with Macbeth.

According to later tradition, Duncan's two young sons were sent away for greater safety — exactly where is the subject of debate. According to one version, Malcolm's brother Donald was sent to the Isles; and Malcolm was sent to England; based on Fordun's account, it came to be assumed that Malcolm passed most of Macbeth's seventeen-year reign in the Kingdom of England at the court of Edward the Confessor. It is also possible that Malcolm went into exile at the court of Thorfinn Sigurdsson, Earl of Orkney, an enemy of Macbeth's family. Ireland and Strathclyde may be other candidates, but neither the place of exile nor, in fact, exile itself, are certainties.

An English invasion in 1054, with Siward, Earl of Northumbria in command, had as its goal the installation of one "Máel Coluim, son of the king of the Cumbrians". This Máel Coluim was traditionally identified with the later Malcolm III. The interpretation derives from the Chronicle attributed to John of Fordun, as well as from earlier sources such as William of Malmesbury. The latter reported that Macbeth was killed in the battle by Siward, but it is known that Macbeth outlived Siward by two years. A.A.M. Duncan argued in 2002 that, using the Anglo-Saxon Chronicle entry as their source, later writers innocently misidentified "Máel Coluim" with the later Scottish king of the same name. Duncan's argument has been supported by several subsequent historians specialising in the era, such as Richard Oram, Dauvit Broun and Alex Woolf. It has also been suggested that Máel Coluim may have been a son of Owain Foel, British king of Strathclyde perhaps by a daughter of Malcolm II, King of Scotland.

In 1057, various chroniclers report the death of Macbeth at Malcolm's hand, on 15 August 1057 at Lumphanan in Aberdeenshire. Macbeth was succeeded by his stepson Lulach, who was crowned at Scone, probably on 8 September 1057. Lulach was killed by Malcolm, "by treachery", near Huntly on 23 April 1058. After this, Malcolm became king, perhaps inaugurated on 25 April 1058, although only John of Fordun reports this.

If Orderic Vitalis is to be relied upon, in the time of Edward the Confessor Malcolm was betrothed to the English king's kinswoman Margaret, and it is possible this happened when he visited England in 1059. If a marriage agreement was made in 1059, it did not stop the Scots plundering Lindisfarne in 1061. It was common practice in medieval Gaelic-speaking societies for kings to launch an invasion, the so-called crech ríg, of a neighbour soon after taking power, and the Lindisfarne raid may have been used to boost the stability of the new regime. Since the invasion affected directly only the territory of the rulers of Bamburgh, it is unlikely to have particularly bothered either King Edward or the ealdorman of Northumbria in York, Tostig Godwinson, who at that time on pilgrimage to Rome and who did not enjoy a good relationship with the Bamburgh family. Malcolm may have had specific political motives. For instance, it has been suggested that he may have been trying to advance the position of Gospatric, his possible cousin, at the expense of the ruling Eadwulfing family. It has also been suggested that the raid may have been part of a dispute about the status of Strathclyde.