Clan Mackenzie (Scottish Gaelic: Clann MacCoinnich [ˈkʰl̪ˠãũn̪ˠ max'kɤNʲiç]) is a Highland Scottish clan associated with Kintail and Ross-shire. Its chiefs trace their lineage to the 12th century, though the earliest recorded chief is Alexander Mackenzie of Kintail, who died after 1471. The clan supported Robert the Bruce during the Wars of Scottish Independence, but later feuded with the Earls of Ross.

During the 15th and 16th centuries, Clan Mackenzie participated in several feuds with neighboring clans. In the 17th century, their chief was granted the title Earl of Seaforth, and the clan supported the Royalists in the Scottish Civil War. They backed the Jacobites in 1715 but were divided in 1745, with their chief, Kenneth Mackenzie, Lord Fortrose, supporting the British government, while George Mackenzie, 3rd Earl of Cromartie, joined the Jacobites. Clan Mackenzie has a chief that is recognized by the Court of the Lord Lyon, and the Lord Lyon King of Arms, who is the heraldic authority in Scotland.

The MacKenzies are believed to have the same ancestry as the Matheson and Anrias clans. All three are said to be descended from Gilleoin of the Aird, a Gaelic dynast who lived in the early 12th century. Another theory is that all three are descended from the thirteenth century Kermac Macmaghan. The chiefs of the Clan Mackenzie are said to have been settled at their great stronghold on Eilean Donan by 1297.

All of the earliest traditional Clan Mackenzie histories claim descent from a Fitzgerald progenitor. These histories include those by John Mackenzie of Applecross (died c.1684/5), George Mackenzie, 1st Earl of Cromartie (died 1714) and the unpublished Letterfearn, Ardintoul and Allangrange manuscripts. It is believed that all of these histories ultimately derive from a single manuscript created by William MacQueen, Parson of Assynt in 1576, now lost. Alexander Mackenzie followed the Fitzgerald theory for the first edition of his History of the Mackenzies in 1879, but abandoned it in his later 1894 edition based on the intervening publication of genealogies contained in MS 1467.

In the 14th century during the Wars of Scottish Independence the Clan Mackenzie is said to have been among the clans who fought on the side of Robert the Bruce at the Battle of Inverurie (1308) against the forces of the Clan Comyn who were rivals to the throne. Chief Iain Mac Coinnich is said to have led a force of five hundred Mackenzies at the Battle of Bannockburn in 1314 where the English were defeated.

Later in the 14th century, the Mackenzies are said to have become involved in battles against their powerful neighbour the Earl of Ross and their allies. This resulted in the capture and subsequent execution of chief Kenneth Mackenzie in 1346. Soon after this it appears that his successor as chief of the clan Mackenzie was living in an island castle in Loch Kinellan near Strathpeffer in Easter Ross and it was from this base that the clan was to advance westward once again to Kintail.

An early genealogy of the Mackenzies appears in MS 1467, but the earliest contemporary record of a living Mackenzie is of Alexander Mackenzie of Kintail (Alexandro McKennye de Kintaill) who appeared in two supplications for papal dispensation in 1465 and 1466, and was listed as a witness to a charter by John of Islay, Earl of Ross, and Lord of the Isles on 4 November 1471. The earliest known likeness of a Mackenzie is that of Sir Kenneth Mackenzie (d. 7 February 1491/1492), whose effigy can be seen at Beauly Priory. He is the first Mackenzie to be buried at Beauly Priory. There is no reliable evidence to support the traditional assertion that previous members of his family were buried at Iona.

In 1452 a force of tribes loyal to Mackenzie of Kintail took hostage a relative of the Earl of Ross. This resulted in the Battle of Bealach nam Broig which was fought to the north-west of Ben Wyvis. The Clan Munro and their septs the Dingwalls rescued the Ross hostage but won a hollow victory, with a great loss of their own men.