Katharevousa (καθαρεύουσα) is a form of the Greek language, created during the early 19th century by Adamantios Korais (1748-1833). A graduate of the university of Montpellier in 1788, Korais spent most of his life as an expatriate in Paris. A classical scholar, Korais was repelled by the Byzantine influence in Greek society and was a fierce critic of the ignorance of the clergy and their subservience to the Ottoman Empire. He realized that education was a precursor to Greek liberation.

The 'purified' Greek was to be the midpoint between Ancient Greek and Modern (of that time). Katharevousa actually contained archaicised forms of modern words, purged of 'non-Greek' vocabulary from other European languages and Turkish and a simplified, archaic grammar.

The purpose of its creation was to mediate the struggle between the 'archaists' (those scholars who preferred Ancient Greek to Modern) and the 'modernists' (those who preferred Modern Greek). One reason the Archaists preferred Ancient Greek was that Modern Greek includes many Latin, Italian and Turkish loan words; and Greece then was a part of the Ottoman Empire). The name Katharevousa means more or less 'clean one', implying that it is a clean form of Greek, without foreign influences, maybe as it would hypothetically have evolved from Ancient Greek had there been no foreign influence.

Soon after the Second World War a long-lasting political debate became associated with the language issue, with the communists and leftists supporting Modern Greek while the conservative right supported Katharevousa.

In later years, Katharevousa was used only for official and formal purposes (such as politics, letters, official documents, and newscasting) while Dhimotiki, (δημοτική) 'demotic' or popular Greek, was the daily language. However, by the end of the 20th century it had become obsolete even for this limited use, having been displaced by Dhimotiki.

In 1981 Dimotiki became the official form of the Greek language by the PASOK (Panhellenic Socialist Movement) political party.