The Kingdom of Scotland was a sovereign state in northwest Europe, traditionally said to have been founded in 843. Its territories expanded and shrank, but it came to occupy the northern third of the island of Great Britain, sharing a land border to the south with the Kingdom of England. During the Middle Ages, Scotland engaged in intermittent conflict with England, most prominently the Wars of Scottish Independence, which saw the Scots assert their independence from the English. Following the annexation of the Hebrides and the Northern Isles from Norway in 1266 and 1472 respectively, and the capture of Berwick by England in 1482, the territory of the Kingdom of Scotland corresponded to that of modern-day Scotland, bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the southwest.

In 1603, James VI of Scotland became King of England, joining Scotland with England in a personal union. In 1707, during the reign of Queen Anne, the two kingdoms were united to form the Kingdom of Great Britain under the terms of the Acts of Union. The Crown was the most important element of Scotland's government. The Scottish monarchy in the Middle Ages was a largely itinerant institution, before Edinburgh developed as a capital city in the second half of the 15th century. The Crown remained at the centre of political life and in the 16th century emerged as a major centre of display and artistic patronage, until it was effectively dissolved with the 1603 Union of Crowns. The Scottish Crown adopted the conventional offices of western European monarchical states of the time and developed a Privy Council and great offices of state. Parliament also emerged as a major legal institution, gaining an oversight of taxation and policy, but was never as central to the national life. In the early period, the kings of the Scots depended on the great lords—the mormaers and toísechs—but from the reign of David I, sheriffdoms were introduced, which allowed more direct control and gradually limited the power of the major lordships.

In the 17th century, the creation of Justices of Peace and Commissioners of Supply helped to increase the effectiveness of local government. The continued existence of courts baron and the introduction of kirk sessions helped consolidate the power of local lairds. Scots law developed in the Middle Ages and was reformed and codified in the 16th and 17th centuries. Under James IV the legal functions of the council were rationalised, with Court of Session meeting daily in Edinburgh. In 1532, the College of Justice was founded, leading to the training and professionalisation of lawyers. David I is the first Scottish king known to have produced his own coinage. After the union of the Scottish and English crowns in 1603, the Pound Scots was reformed to closely match sterling coin. The Bank of Scotland issued pound notes from 1704. Scottish currency was abolished by the Acts of Union 1707; however, Scotland has retained unique banknotes to the present day.

Geographically, Scotland is divided between the Highlands and Islands and the Lowlands. The Highlands had a relatively short growing season, which was even shorter during the Little Ice Age. Scotland's population at the start of the Black Death was about 1 million; by the end of the plague, it was only half a million. It expanded in the first half of the 16th century, reaching roughly 1.2 million by the 1690s. Significant languages in the medieval kingdom included Gaelic, Old English, Norse and French; but by the early modern era Middle Scots had begun to dominate. Christianity was introduced into Scotland from the 6th century. In the Norman period the Scottish church underwent a series of changes that led to new monastic orders and organisation. During the 16th century, Scotland underwent a Protestant Reformation that created a predominately Calvinist national kirk. There were a series of religious controversies that resulted in divisions and persecutions. The Scottish Crown developed naval forces at various points in its history, but often relied on privateers and fought a guerre de course. Land forces centred around the large common army, but adopted European innovations from the 16th century; and many Scots took service as mercenaries and as soldiers for the English Crown.

From the 5th century on, north Britain was divided into a series of petty kingdoms. Of these, the four most important were those of the Picts in the north-east, the Scots of Dál Riata in the west, the Britons of Strathclyde in the south-west and the Anglian kingdom of Bernicia (which united with Deira to form Northumbria in 653) in the south-east, stretching into modern northern England.

In 793, ferocious Viking raids began on monasteries such as those at Iona and Lindisfarne, creating fear and confusion across the kingdoms of north Britain. Orkney, Shetland and the Western Isles eventually fell to the Norsemen. In a decisive battle in 839, the king of the Picts, Uuen, and the king of Dál Riata, Áed, were killed by Vikings. This led to a period of instability, which culminated in the rise of Cínaed mac Ailpín (Kenneth MacAlpin) as "king of the Picts" in the 840s (traditionally dated to 843), and brought to power the House of Alpin.

Under the House of Alpin, there was a long-term process of Gaelicisation of the Pictish kingdoms, which adopted Gaelic language and customs. There was also a merger of the Gaelic (Scots) and Pictish kingdoms, although historians debate whether it was a Pictish takeover of Dál Riata, or vice-versa. When he died as king of the combined kingdom in 900, one of Kenneth's successors, Domnall II (Donald II), was the first man to be called rí Alban (King of Alba). The Latin term Scotia would increasingly be used to describe the heartland of these kings, north of the River Forth, and eventually the entire area controlled by its kings would be referred to, in English, as Scotland. The long reign (900–942/3) of Donald's successor Causantín (Constantine II) is often regarded as the key to formation of the Kingdom of Alba/Scotland, and he was later credited with bringing Scottish Christianity into conformity with the Catholic Church.

Máel Coluim I (Malcolm I) (r.  c. 943–954) is believed to have annexed the Kingdom of Strathclyde, over which the kings of Alba had probably exercised some authority since the later 9th century. His successor, Indulf the Aggressor, was described as the King of Strathclyde before inheriting the throne of Alba; he is credited with later annexing parts of Lothian, including Edinburgh, from the Kingdom of Northumbria. The reign of David I has been characterised as a "Davidian Revolution", in which he introduced a system of feudal land tenure, established the first royal burghs in Scotland and the first recorded Scottish coinage, and continued a process of religious and legal reforms.