The 18th century lasted from 1701 to 1800 in the Gregorian calendar.

However, Western historians may sometimes specifically define the 18th century otherwise for the purposes of their work. For example, the "short" 18th century may be defined as 1715–1789, denoting the period of time between the death of Louis XIV of France and the start of the French Revolution with an emphasis on directly interconnected events.

To historians who expand the century to include larger historical movements, the "long" 18th century may run from the Glorious Revolution of 1688 to the battle of Waterloo in 1815 or even later. During the 18th century, the Enlightenment culminated in the French, Haitian and American revolutions. Philosophy and science increased in prominence. Philosophers were dreaming about a better age without the Christian fundamentalism of earlier centuries. This dream turned into a nightmare during the terror of Maximilien Robespierre in the early 1790s. At first, the monarchies of Europe embraced enlightenment ideals, but with the French revolution, they were on the side of the counterrevolution.

Great Britain became a major power worldwide with the defeat of France in the Americas in the 1760s and the conquest of large parts of India. However, Britain lost much of her North American colonies after the American revolution. The industrial revolution started in Britain around the 1770s. Despite its modest beginnings in the 18th century, it would radically change human society and the geology of the surface of the earth.