James VI and I (James Charles Stuart; 19 June 1566 – 27 March 1625) was King of Scotland as James VI from 24 July 1567 and King of England and Ireland as James I from the union of the Scottish and English crowns on 24 March 1603 until his death in 1625. Though he long attempted to get both countries to adopt a closer political union, the kingdoms of Scotland and England remained sovereign states, with their own parliaments, judiciaries, and laws, ruled by James in personal union.

James was the son of Mary, Queen of Scots, and a great-great-grandson of Henry VII, King of England and Lord of Ireland, and thus a potential successor to all three thrones. He acceded to the Scottish throne at the age of thirteen months, after his mother was forced to abdicate. Although his mother was a Catholic, James was raised as a Protestant. Four regents governed during his minority, which ended officially in 1578, though he did not gain full control of his government until 1583. In 1589, he married Anne of Denmark. Three of their children survived to adulthood: Henry Frederick, Elizabeth, and Charles. In 1603, James succeeded his cousin Elizabeth I, the last Tudor monarch of England and Ireland, who died childless. He reigned in all three kingdoms for 22 years, a period known as the Jacobean era, until his death in 1625. After the Union of the Crowns, he based himself in England from 1603, returning to Scotland only once, in 1617, and styled himself "King of Great Britain and Ireland". He advocated for a single parliament for England and Scotland. In his reign, the Plantation of Ulster and English colonisation of the Americas began.

At 57 years and 246 days, James's reign in Scotland was the longest of any Scottish monarch. He achieved most of his aims in Scotland but faced great difficulties in England, including the Gunpowder Plot in 1605 and conflicts with the English Parliament. Under James, the "Golden Age" of Elizabethan literature and drama continued, with writers such as William Shakespeare, John Donne, Ben Jonson, and Francis Bacon contributing to a flourishing literary culture. James was a prolific writer, authoring works such as Daemonologie (1597), The True Law of Free Monarchies (1598), and Basilikon Doron (1599). He sponsored the translation of the Bible into English (later named after him, the Authorized King James Version), and the 1604 revision of the Book of Common Prayer. Contemporary courtier Anthony Weldon claimed that James had been termed "the wisest fool in Christendom" (wise in small things, foolish otherwise), an epithet associated with his character ever since. Since the latter half of the 20th century, historians have tended to revise James's reputation and treat him as a serious and thoughtful monarch. He was strongly committed to a peace policy, and tried to avoid involvement in religious wars, especially the Thirty Years' War that devastated much of Central Europe. He tried but failed to prevent the rise of hawkish elements in the English Parliament who wanted war with Spain. The first English king of the House of Stuart, he was succeeded by his second son, Charles I.

James was the only son of Mary, Queen of Scots, and her second husband, Henry Stuart, Lord Darnley. Mary and Darnley were great-grandchildren of Henry VII of England through Margaret Tudor, the older sister of Henry VIII. Mary's rule over Scotland was insecure, and she and her husband, being Roman Catholics, faced a rebellion by Protestant noblemen. During Mary's and Darnley's difficult marriage, Darnley secretly allied himself with the rebels and conspired in the murder of the queen's private secretary, David Rizzio, just three months before James's birth.

James was born on 19 June 1566 at Edinburgh Castle, and as the eldest son and heir apparent of the monarch automatically became Duke of Rothesay and Prince and Great Steward of Scotland. Five days later, the English diplomat Henry Killigrew saw the queen, who had not fully recovered and could only speak faintly. The baby was "sucking at his nurse" and was "well proportioned and like to prove a goodly prince". He was baptised "Charles James" or "James Charles" on 17 December 1566 in a Catholic ceremony held at Stirling Castle. His godparents were Charles IX of France (represented by John, Count of Brienne), Elizabeth I of England (represented by the Francis Russell, Earl of Bedford), and Emmanuel Philibert, Duke of Savoy (represented by ambassador Philibert du Croc). Mary refused to let the Archbishop of St Andrews, whom she referred to as "a pocky priest", spit in the child's mouth, as was then the custom. The subsequent entertainment, devised by Frenchman Bastian Pagez, featured men dressed as satyrs and sporting tails, to which the English guests took offence, thinking the satyrs "done against them".

Lord Darnley was murdered on 10 February 1567 at Kirk o' Field, Edinburgh, perhaps in revenge for the killing of Rizzio. James inherited his father's titles of Duke of Albany and Earl of Ross. Mary was already unpopular, and her marriage on 15 May 1567 to James Hepburn, Earl of Bothwell, who was widely suspected of murdering Darnley, heightened widespread bad feeling towards her. In June 1567, Protestant rebels arrested Mary and imprisoned her in Lochleven Castle; she never saw her son again. She was forced to abdicate on 24 July 1567 in favour of the infant James and to appoint her illegitimate half-brother James Stewart, Earl of Moray, as regent. This made James the third consecutive Scottish monarch to ascend to the throne as an infant.

The care of James was entrusted to the Earl and Countess of Mar, "to be conserved, nursed, and upbrought" in the security of Stirling Castle. James was anointed King of Scotland at the age of thirteen months at the Church of the Holy Rude in Stirling, by Adam Bothwell, Bishop of Orkney, on 29 July 1567. The sermon at the coronation was preached by John Knox. In accordance with the religious beliefs of most of the Scottish ruling class, James was brought up as a member of the Protestant Church of Scotland, the Kirk. The Privy Council selected George Buchanan, Peter Young, Adam Erskine (lay abbot of Cambuskenneth), and David Erskine (lay abbot of Dryburgh) as James's preceptors or tutors. As the young king's senior tutor, Buchanan subjected James to regular beatings but also instilled in him a lifelong passion for literature and learning. Buchanan sought to turn James into a God-fearing, Protestant king who accepted the limitations of monarchy, as outlined in his treatise De Jure Regni apud Scotos.

In 1568, Mary escaped from Lochleven Castle, leading to several years of sporadic violence. The Earl of Moray defeated Mary's troops at the Battle of Langside, forcing her to flee to England, where she was subsequently kept in confinement by Elizabeth. On 23 January 1570, Moray was assassinated by James Hamilton of Bothwellhaugh. The next regent was James's paternal grandfather, Matthew Stewart, Earl of Lennox, who was carried fatally wounded into Stirling Castle a year later after a raid by Mary's supporters. His successor, the Earl of Mar, "took a vehement sickness" and died on 28 October 1572 at Stirling. Mar's illness, wrote James Melville, followed a banquet at Dalkeith Palace given by James Douglas, Earl of Morton.